Fire Scene Evidence Collection Guide

FAQ

Documentation


Q: How do I document the transfer of evidence from one container to another?

A: Be sure to note the transfer in your report and explain why the transfer was made. Documenting the transfer with a series of photos is suggested.

Q: Do I need to take pictures before I move or collect the evidence?

A: Yes. Documentation prior to and during the collection of evidence is crucial to prevent spoliation.




PPE and Collection Tools


Q: Are nitrile gloves better than latex gloves?

A: It is the investigator’s preference as to which type of disposable glove to use to collect evidence. The important point is to make sure disposable evidence gloves are being worn to collect evidence and that they are changed after each piece of evidence is collected. That said, nitrile gloves protect against a broader range of chemicals and petroleum-based products. Nitrile gloves are also more resistant to punctures and tears. But, some people find that latex gloves offer a better fit and provide a bit more dexterity than nitrile gloves. However, some people are allergic to latex.

Q: When should I “double-glove” when obtaining evidence?

A: It is not necessary to double glove to collect evidence. If you find your gloves are tearing, consider switching to nitrile gloves, which are more resistant to tears. Some investigators put on several pairs of gloves and then remove the top pair, after collection of each piece of evidence, which exposes a new, clean pair of gloves for the next sample to be collected. Be aware that, if you leave the same pair of snug-fitting gloves on for an extended period of time, your hand can become very wet with perspiration. The sweat sticks neatly onto the ridges on your fingertips and you can transfer your prints onto a clean surface.

Q: When should I consider using plastic evidence-gathering tools as opposed to metallic?

A: Use plastic tools whenever the object you are collecting with a metallic tool might leave a toolmark (impressed or striated), which would compromise the integrity of the evidence. In addition, if there is a question of the elemental composition of the evidence, then metallic tools should be avoided. For example, if you are collecting soil for analysis, depending on the type of analysis to be done on the evidence, metallic tools should not be used because they may chemically interact with compounds found in the soil. It is always a good idea to call the lab ahead of time if there is a question as to whether or not to use metallic tools.




Comparison Samples


Q: What is the difference between a comparison sample and a control sample?

A: Simply put, a comparison sample is any material or liquid collected at a fire scene that is collected in an unburned and/or protected state for the purposes of establishing the chemical and physical properties of the material in its natural state in that environment. A control sample is when known liquids or known material (such as carpet) are obtained in their pristine form from a source such as a manufacturer or a retailer. So, in the case of carpet, the questioned sample might be burned carpet from the scene, the comparison sample would be the same carpet installed in that location but unburned, and the control sample would be the same carpet obtained directly from the manufacturer’s or retailer’s stock. When labeling your evidence, if you collect material or liquid from a fire scene with the intent of comparing it with a questioned sample from that scene, it is a comparison sample.

Q: Is it necessary to collect a comparison sample?

A: A comparison sample can be vital for the laboratory in specific cases because it can assist in establishing what compounds are naturally occurring in a material at that location. However, a comparison sample should be unburned, soot free, and NOT from the room of origin. In many fire scenes, there is not a sample that meets those guidelines and therefore no comparison sample should be collected. In that case, simply note on your report that a comparison sample was not available.




Evidence Packaging


Q: What are the best evidence containers for fire debris analysis?

A: Appropriate containers for fire debris evidence include clean, unused, lined metal paint containers (which are available in pint, quart, gallon, and five-gallon sizes) and nylon fire debris bags (which also come in varying sizes).

Q: What if the fire debris evidence doesn’t fit in a metal can?

A: Nylon fire debris bags can be used for larger evidence items that don’t fit in a metal can. These nylon fire debris bags are available in varying sizes to accommodate larger items of evidence.

Q: I don’t have a metal can or nylon fire debris bag to package evidence that may contain an ignitable liquid. Can it put the item in a plastic or paper bag and then transfer it to a metal can or nylon bag?

A: You should take your cans every time you respond to a fire scene and have sufficient inventory for your typical workload. It is a good idea to have nylon bags ready as a backup, especially if space in your toolkit or vehicle is an issue. However, in that rare instance when you run out of cans/bags or an extraordinary circumstance occurs, the preferred method of temporary packaging is a paper bag. Plastic bags should never be used, as they contain many interfering products. Remember, the paper bags are only a temporary container, and the evidence should be re-packaged into a metal can or nylon bag immediately. Completely remove the evidence from the paper bag, and either discard the paper bag, or tape it to the outside of the metal can or nylon bag. Make sure you notify the laboratory that the evidence was previously packaged in paper and for how long.

Q: Why do I have to leave 1/3 headspace in a metal can holding evidence that may contain ignitable liquids?

A: In order for the laboratory to analyze the fire debris samples, a minimum of a 1/3 headspace is needed to perform the passive adsorption technique. Please do not fill your fire debris evidence to the top of the can; this will negatively affect the laboratory testing. When in doubt, use a larger container or split your sample into multiple containers.

Q: What is the best way to preserve and package samples of ignitable liquids?

A: There are two ways to properly collect ignitable liquids:

  1. Liquids can be placed into glass vials with a Teflon-coated top, which prevents the liquid from leaking.
  2. A few drops of the liquid can be placed on white, unprinted (non-inked) paper towels, and then those towels placed inside a metal paint can. Do not pour more than a tablespoon of an ignitable liquid into a metal container without an absorbent.

Q: When collecting fire debris evidence, should the latex/nitrile/PVC gloves worn by the person collecting the debris be included in the evidence container with the sample?

A: No. They will contaminate the collected evidence. Some of these gloves are made from heavy petroleum distillates and, therefore, may create background interference during the fire debris analysis. Source: Stauffer, Eric, Julia A. Dolan, and Reta Newman. Fire Debris Analysis. Academic Press, 2007.

Q: May I submit fire debris evidence in lined paint cans?

A: Yes. Many laboratories recommend lined and/or unlined cans for fire debris. The advantage of lined cans is that they resist rust and corrosion. Source: Mann, Dale. “In Search of the Perfect Container for Fire Debris Evidence.” Fire and Arson Investigator, April 2000, pp. 21-25.

Q: What’s the best way to preserve and package pieces of adhesive/duct/masking tape for evidence?

A: It is always best to leave the tape on the item it is adhered to and submit the entire substrate with the tape still attached. If the tape is wadded up, you can place the wad in a can and allow the laboratory take the layers apart while looking for trace evidence. If the tape cannot be left on item for submission, take great care when you remove it — avoid tearing or stretching the tape. If you can, carefully cut the tape off of the item, leaving the layers mostly intact, as opposed to unwinding the tape from the item. In any case, note the cuts that you made. Submit the tape with the adhesive side down on clean, colorless and relatively rigid plastic sheets. Most tapes can be preserved on polypropylene sheet protectors, although some adhesives may react with the polypropylene. You may also use ”release paper” (this is the type of paper that is used as a sticker backing, available in some craft stores). Do not use acetate sheet protectors or paper bags. Clean, clear small panes of glass are also acceptable as long as you package carefully to prevent the glass from breaking. Consult your laboratory prior to collection if you have any questions on acceptable collection methods or preservation substrates.

Q: How do I know when to air dry a wet object and when not to?

A: Items to be examined for ignitable liquid residue should not be air dried before packaging. Air drying allows volatile organic compounds (VOCs) the opportunity to evaporate. These compounds are what are analyzed in ignitable liquids testing. Therefore, if the VOCs are allowed to evaporate, test results may be compromised. If ignitable liquid residue testing is to be performed, the wet item should be collected without air drying and placed in an airtight container, such as a new, unused one gallon metal paint can. Transport the item as soon as possible to the laboratory and inform the laboratory that the material in the container is wet. Items undergoing other types of examination (such as DNA, trace, fingerprint, or document examination) are typically air dried prior to packaging at room temperature, away from direct heat, sunlight, and drafts. Biological evidence (ie: blood, saliva, semen, other bodily fluids, DNA) must be air dried prior to packaging or it may putrefy and therefore lose its evidentiary value. The air drying issue becomes more complicated if evidence will undergo multiple testing protocols where the air drying procedure differs (eg: Molotov cocktail glass bottle stained with blood to be examined for DNA and for ignitable liquid residue). In these cases, consult your laboratory. Typically, the laboratory will advise you to collect the item in an airtight container and bring it to the lab immediately so that ignitable liquids testing can be performed promptly and then the item air dried at the lab in preparation for other types of testing.




Fire Debris and Ignitable Liquids


Q: What is the best way to obtain ignitable liquid evidence from a suspect’s hands?

A: Unfortunately, there is not yet a reliably effective way to collect possible ignitable liquid residues from a suspect’s hands. In the field, swabbing the suspect’s hands with a few large, sterile, cotton gauze pads is an option, although it is not always effective. To swab the hands, heavily moisten the sterile gauze pads with isopropyl alcohol and swab the palms and fingers. Place the moist pads in a metal can, label and seal appropriately. In some instances, the isopropyl alcohol will act as a solvent and lift the gasoline from the skin and transfer it to the gauze pad. Send comparison samples of the alcohol-soaked pads to the lab as well. Be certain to tell the lab what you did and how you retrieved the sample. Remember that the suspect’s outer layer of clothing can be a fruitful place for ignitable liquid residue to deposit and thus be identified through laboratory analysis. Therefore, collect the outer layer of clothing whenever possible.

Q: How do I collect what appears to be an ignitable liquid floating on a puddle of water?

A: There are three options that are typically used to sample possible ignitable liquid floating on water.

  1. Siphoning. Siphon off some of the liquid (1-2 teaspoons max) with a clean, disposable pipette. Transfer the liquid in the pipette onto a clean, cotton gauze pad and place in a metal can.
  2. Gauze pad. Use a clean, cotton gauze pad to soak up the liquid. The gauze pad can then be placed a metal container.
  3. Paper towels. Use clean, unused, individually packaged rolls of white (no print) paper towels. Use the paper towel to soak up the suspected liquid and place the towel inside a metal can.

It is always a good idea to check with your laboratory to see if there is a method they prefer. Please note that ignitable liquid samples should NOT be dried before packaging. Be aware that gauze pads, maxi pads, and tampons can contain naturally occurring interfering substances. If you do use one of these products, submit a clean unopened one to the laboratory for comparison.

Q: Can the laboratory identify an end-use product of an ignitable liquid from the results of analysis of the fire debris or neat liquid?

A: No. Crude oil is distilled into many fractions. These distillates are then separated into categories based on the number of carbon atoms in the straight hydrocarbon chain. The fractions are sold to one or more companies that will market the distillate as different end-use products. For example, a medium petroleum distillate, with a range of about C8–C13, can be sold as paint thinner, mineral spirits, and/or charcoal lighter fluid. Source: interFIRE. “Part 2: Ignitable Liquids: Petroleum Distillates, Petroleum Products, and Other Stuff.” Online Training Module, 2013: http://www.interfire.org/features/ourchangingworld2.asp

Q: Can the laboratory distinguish between different types/grades of gasoline?

A: No. The laboratory cannot distinguish from different brands (ie: Exxon, Texaco) nor different octane (87, 91, 93) ratings of gasoline.

Q: What if I want multiple analyses that may conflict with each other? Do I have to choose?

A: It is vital you speak with your laboratory and explain the type of evidence you have, and the tests you would like to have performed. The laboratory will be able to determine in what order the tests need to be performed. In most cases, you don’t have to give something up. Most laboratories have considered this possibility of multiple examination types and have a way of handling it. Make sure to note the analyses that you want performed on a piece of evidence on your evidence transmittal paperwork and on the containers. In situations where evidence may be destroyed, you may have to call the lab for advice on how they would like it packaged. For example, if you would like DNA analysis done on a piece of evidence (which requires breathable packaging) and fire debris analysis (which requires air-tight packaging), the lab may tell you to package it in an air-tight container and bring it to the lab immediately so that the fire debris analysts can collect their evidence before the item is taken out of the air-tight container and dried for subsequent DNA analysis.

Q: What type of ignitable liquids testing can be performed on fire debris?

A: Fire debris can be tested for ignitable liquids using gas chromatography mass spectrometry. This test can determine the classification of the ignitable liquid

Q: What are the best evidence containers for fire debris analysis?

A: Appropriate containers for fire debris evidence include clean, unused, lined metal paint containers (which are available in pint, quart, gallon, and five-gallon sizes) and nylon fire debris bags (which also come in varying sizes).

Q: What do I do if an item I want tested for ignitable liquid residue is too large to fit in a metal can?

A: Nylon fire debris bags can be used for larger evidence items that don’t fit in a metal can. These nylon fire debris bags are available in varying sizes to accommodate larger items of evidence.

Q: I don’t have a metal can to package clothing that has an ignitable liquid on it. Can I put it in a plastic or paper bag and then transfer it to a metal can? And if I do, would it be wise to submit the temporary container in a metal can as well?

A: Nylon fire debris bags, which can be purchased in large sizes, can also be used for clothing that may contain an ignitable liquid. Your toolkit or vehicle should be stocked with larger sizes of metal paint containers and nylon fire debris bags. If you do not have a metal can or nylon bag large enough, the preferred method of temporary packaging is a paper bag. Plastic bags should never be used, as they contain many interfering products. Remember, the paper bags are only a temporary container, and the evidence should be re-packaged into a metal can or nylon bag immediately. Completely remove the evidence from the paper bag, and either discard the paper bag, or tape it to the outside of the metal can or nylon bag. Make sure you notify the laboratory that the evidence was previously packaged in paper and for how long.

Q: Why do I have to leave 1/3 headspace in a metal can holding evidence that may contain ignitable liquids?

A: In order for the laboratory to analyze the fire debris samples, a minimum of a 1/3 headspace is needed to perform the passive adsorption technique. Please do not fill your fire debris evidence to the top of the can; this will negatively affect the laboratory testing. When in doubt, use a larger container or split your sample into multiple containers.

Q: What key factors do I need to know when requesting and working with accelerant detection K-9 (AK-9) team?

A: Check with your local AK-9 Handler for any specific guidelines, but as a general rule, consider the following factors: any hazardous materials or illegal drugs at the scene, fire suppression foam obscuring firm footing, unstable flooring, risk of collapse, electrical service still connected, and any physical barriers or obstructions preventing access.

Q: If I utilize an accelerant detection K-9 at my scene, what can I do to ensure the best samples are being forwarded to the lab?

A: Check with your local AK-9 Handler for any specific guidelines but, as a general rule, keep any gasoline power tools away from the area of origin, do not re-fill gasoline-powered positive pressure ventilation fans at the door of the structure, and provide a neutral site far enough away from the scene for the AK-9 team to conduct a secondary examination of samples collected.

Q: How do I know when to air dry a wet object and when not to?

A: Items to be examined for ignitable liquid residue should not be air dried before packaging. Air drying allows volatile organic compounds (VOCs) the opportunity to evaporate. These compounds are what are analyzed in ignitable liquids testing. Therefore, if the VOCs are allowed to evaporate, test results may be compromised. If ignitable liquid residue testing is to be performed, the wet item should be collected without air drying and placed in an airtight container, such as a new, unused one gallon metal paint can. Transport the item as soon as possible to the laboratory and inform the laboratory that the material in the container is wet.




DNA


Q: Does Luminol ruin the chances for subsequent DNA analysis?

A: No. Studies, beginning in 1991, have shown that Luminol does not harm DNA and subsequent DNA analysis.

However, if Luminol, or any other liquid blood enhancement techniques are sprayed on the bloodstains in excess, it may wash away (physically remove) trace amounts of blood and DNA. A paper by Quinones et al. (2007) also suggests that some formulations (with perborate) may damage DNA and, therefore, subsequent DNA analysis: “… that in vivo perborate damages DNA to a greater extent than hydrogen peroxide, possibly due to its greater penetration of cells …”. So, if Luminol is used sparingly when spraying and the Luminol formulation is not the one that is made with perborate, the use of Luminol will not affect DNA analysis.

Sources:

Q: Does Superglue® ruin the chances for subsequent DNA analysis?

A: No, the use of Superglue (chemical name: cyanoacrylate) does not hinder subsequent DNA analysis. As early as 1993 and using the older method of DNA analysis called RFLP (restriction fragment length polymorphism), cyanoacrylate was shown not to interfere with subsequent DNA analysis. And in 2009, it was shown that even delicate touch DNA from post-blast bomb fragments could be exposed to cyanoacrylate and DNA analysis was still possible.

Sources:

  • Bille, T.W., C. Cromartie, and M. Farr. “Effects of Cyanoacrylate Fuming, Time After Recovery, and Location of Biological Material on the Recovery and Analysis of DNA from Post-Blast Pipe Bomb Fragments.” Journal of Forensic Sciences, 54, (5), September 2009: 1059-1067 2009. http://onlinelibrary.wiley.com/doi/10.1111/j.1556-4029.2009.01128.x/full

  • Shipp, E., R. Roelofs, E. Togneri, R. Wright, D. Atkinson, and B. Henry. “Effects of Argon Laser Light, Alternate Source Light, and Cyanoacrylate Fuming on DNA Typing of Human Bloodstains.” Journal of Forensic Sciences, 38 (1), January 1993: 184-191.

Q: Can DNA analysis be done on evidence after it has been exposed to fire?

A: Yes. DNA can be detected after being exposed to heat and fire—within limitation. The DNA cannot be exposed to extreme heat (about 800°C/1400ºF and above) for an extended period of time. Also, DNA can be recovered from Molotov cocktails from both the bottle AND the wick. Source: Tontarski, K.L., et al. “Chemical Enhancement Techniques of Bloodstain Patterns and DNA Recovery after Fire Exposure.” Journal of Forensic Sciences, 54 (1), January 2009: 37-48. https://www.bluestar-forensic.com/pdf/en/AAFS_bloodstain_after_fire_exposure.pdf (See, also, this article reprinted in IAAI’s Fire & Arson Investigator Journal, April 2012, pp. 10-18, with additional information on heat flux.)

Q: I can’t tip off my suspect by asking for a buccal swab. Can I do a trash pull at his house to get a secondary DNA reference?

A: Secondary references may be accepted by the lab. However, to effectively use a secondary reference, there are two considerations:

  1. The chain of custody needs to be solid. The person collecting the secondary reference should observe the suspect using the item (cigarette, soda can, etc.) and discarding the item. The item needs to be immediately recovered, preferably without the item leaving the sight of the collecting officer. An item discarded in a trash can without the discarding of the item being directly observed by the collecting officer leaves too much doubt about who deposited the DNA on the item (even if the suspect lives alone).
  2. A single source DNA profile must be obtained. Mixed DNA profiles (more than one contributor) cannot be used as secondary references. The best types of secondary references typically include cigarette butts, drinking cans/bottles, chewing gum, saliva, or something containing a body fluid (such as used Kleenex with blood/mucus/semen). Clothing often contains a mixed DNA profile, so it should be used only as a last resort.

As always, check with the lab that you are submitting the evidence to for their particular requirements.

Q: What’s the best method to swab for DNA?

A: The best way to collect DNA is to send the actual item bearing the DNA to the laboratory and let the DNA analyst collect the sample. But there are situations where the item cannot be sent to the lab (such as concrete flooring, car doors/parts), so the DNA will have to be collected at the scene. You should always check with your laboratory and use the method they recommend. However, the following collection methods are accepted in the industry:

  1. For a wet blood/body fluid stain, use a dry cotton swab and sop up as much of the fluid as possible, concentrating the sample (get as much as you can on one swab vs. many swabs with weak stains).
  2. For dried blood/body fluid, moisten a cotton swab with de-ionized water (you can get this at the drug store) and collect the dried stain (remember to concentrate the stain on as few swabs as possible)
  3. For touch DNA (eg: a car steering wheel, a door knob) use the “double swab method.” Moisten one swab with de-ionized water and leave the other dry. First swab the area with the wet swab, then go over the same area with the dry swab.

All swabs should be placed in a breathable (not plastic) container. A swab box is preferable but the swabs can be replaced in their paper sleeve (their original package) and sealed in a clean envelope. It is best to dry the swabs before packaging by placing them such that you avoid touching the swab end to any surface. This can be done by placing them in the swab box and leaving the top open (be sure the box is in an area where the swabs will be undisturbed and not exposed to any outside sources of DNA). Source: Sweet, D., et al. “An Improved Method to Recover Saliva from Human Skin: The Double Swab Technique.” Journal of Forensic Sciences, 42 (2), March 1997:320-322.




Fingerprints and Impressions


Q: What should be taken into consideration when using magnetic powder as opposed to non-magnetic powder when obtaining latent prints?

A: Magnetic powder is coarser than non-magnetic powder. A heavy application of magnetic powder and multiple passes with the wand could distort the print. When using magnetic powder and the wand, lightly draw the powder a maximum of 3-4 times over the entire area to be lifted.

Q: What can I use to obtain fingerprints on a textured or irregular surface?

A: After dusting the surface, Mikrosil(TM), or a similar casting medium can be spread over the dusted area. Follow the manufacturer’s directions for mixing and preparation. Allow the material to dry, and then gently peel the material away from the object. Place lifting tape over the print to preserve it and attach to a fingerprint card. Advise the lab that this is a reverse print.

Q: What type of material should I use to cast shoe/boot or tire impressions? What can I do to ensure that material (dirt, sand, clay, or loam) will maintain its integrity during the casting process?

A: For casting, the FBI recommends dental stone due to its compressive strength. Dental stone is readily available at dental supply stores. Do not use plaster of Paris; it is too brittle and can break in shipping. Unlike plaster, dental stone does not need any reinforcing and hardens through a chemical process rather than drying. The dental stone is mixed with water, usually using a zip-lock baggie. When enough water is added that the mixture is the consistency of pancake batter, it is poured into the impressions using a piece of cardboard to allow the mixture to gently flow into the impression. Follow the manufacturer’s directions for mixing and preparation. Be certain to allow the cast to completely harden and air dry before packaging.

Before making casts of footwear or tire impressions, be sure to photograph them with a scale and be sure the scale is at the same depth as the bottom of the footwear impression.

Before the dental stone mixture is placed into the impression, the substrate needs to be fortified so that it retains its shape and the detail of the impression.

  1. If the substrate is dry, use acrylic hair spray or spray paint sprayed gently above/over (not into) the impression and allowed to float down into the impression.
  2. If the substrate is wet, sprinkle a little bit of the dry dental stone or talcum powder onto the impression (this is so the wet substrate doesn’t mix with the wet dental stone)
  3. If the impression is in snow, you can use automotive spray primer or Snowprint Wax(TM). This will insulate the snow from the heat caused by the curing of the dental stone (dental stone cures by a chemical reaction that gives off heat). Automotive spray primer or Snowprint Wax are colored and will show of highlights of the impressions on the white snow, therefore another set of photographs should be taken after the automotive spray primer or Snowprint Wax is applied to the impression.

When pouring the dental stone into the impression, be sure to start outside the impression, using a utensil such as a piece of cardboard or other flat surface to deflect the impact of the dental stone hitting the impression, and work the pour to the inside of the impression.

Q: What material can I use to obtain tool mark impressions?

A: An application of Mikrosil(TM) or a similar casting medium can be gently spread over the area. Follow the manufacturer’s directions for mixing and preparation. Allow the material to dry, and then gently peel the material away from the object. Place the casting in a box or can to prevent damage in transit. Advise the lab how you obtained the evidence. If the tool that may have made the impression is located, submit the tool to the lab for a comparison.

Q: What can I do to ensure the material (dirt, sand, clay, or loam) maintains its integrity during the casting process?

A: A light mist application of hairspray to the area will bind loose dirt or sand. Allow a minute or so for the hairspray to dry before casting.

Q: Does Superglue® ruin the chances for subsequent DNA analysis?

A: No, the use of Superglue (chemical name: cyanoacrylate) does not hinder subsequent DNA analysis. As early as 1993 and using the older method of DNA analysis called RFLP (restriction fragment length polymorphism), cyanoacrylate was shown not to interfere with subsequent DNA analysis. And in 2009, it was shown that even delicate touch DNA from post-blast bomb fragments could be exposed to cyanoacrylate and DNA analysis was still possible. Sources:

  • Bille, T.W., C. Cromartie, and M. Farr. “Effects of Cyanoacrylate Fuming, Time After Recovery, and Location of Biological Material on the Recovery and Analysis of DNA from Post-Blast Pipe Bomb Fragments.” Journal of Forensic Sciences, 54, (5), September 2009: 1059-1067 2009. http://onlinelibrary.wiley.com/doi/10.1111/j.1556-4029.2009.01128.x/full

  • Shipp, E., R. Roelofs, E. Togneri, R. Wright, D. Atkinson, and B. Henry. “Effects of Argon Laser Light, Alternate Source Light, and Cyanoacrylate Fuming on DNA Typing of Human Bloodstains.” Journal of Forensic Sciences, 38 (1), January 1993: 184-191.

Q: Can you get latent prints off textured surfaces? Human bodies?

A: It is tricky but it can be done. One method for lifting prints off hard, textured surfaces is using a casting medium. After dusting the surface, Mikrosil(TM) or a similar casting medium can be spread over the dusted area. Follow the manufacturer’s directions for mixing and preparation. Allow the material to dry and then gently peel the material away from the object. Place lifting tape over the print to preserve it and attach to a fingerprint card. Advise the lab that this is a reverse print. Consult your laboratory for other methods or for situations like latent prints on a human body. Be aware that, even if there is not sufficient ridge detail for latent print comparison, the presence of a print will show where the item was touched and touch DNA may be obtainable in that location. Source: Morris, M. “Casting a Wide Net: Lifting Fingerprints from Difficult Surfaces.” Forensic Magazine, January 8, 2005. http://www.forensicmag.com/article/casting-wide-net-lifting-fingerprints-difficult-surfaces




Decontamination


Q: What’s the best way to decontaminate my tools?

A: Thoroughly wash tools with a detergent and water solution followed by two water rinses. A liquid detergent that breaks down oils and grease, such as Dawn, is recommended. At fatal fire scenes, an additional rinse with a 10% bleach in water solution, to eliminate any bodily fluid transfer is recommended after the detergent solution wash. This bleach in water step is followed by two water rinses. Then, wipe the tool with a clean cloth or paper towels and allow the tool to dry thoroughly before storage.




Other Evidence Types


Q: The laboratory my organization uses doesn’t accept a certain kind of evidence I want to collect or perform a test I want to have done. Is there anything I can do?

A: Your laboratory should be a resource for any type of testing that you need and assist you in finding an analyst if they do not perform that type of testing. The following are websites for organizations that may assist you in finding the analyst you need.

International Association for Identification (IAI) website has links to the following disciplines (https://www.theiai.org/forensic_disciplines.php)

You can also contact the American Academy of Forensic Sciences for links to regional forensic organizations and other resources: http://www.aafs.org/forensic-links.

Q: What evidence can I obtain or request analysis for from tape or rope?

A: DNA, trace evidence, and/or a physical/mechanical match may all be possible with rope/cordage and tape evidence. Composition and physical properties or both can also be obtained and compared with known samples. If the rope/cordage or the tape is unusual, a possible end-use may prove useful to the investigation. If there is a knot associated to the rope/cordage, this may also prove to be a useful piece of information. With tape, latent fingerprints may also be present. Evidence that can be obtained from both rope and tape can be a positive identification through a physical match, a class association (“could be from the same source”), or an elimination. If a physical match or "puzzle fit” cannot be done, an association between questioned and known may be possible. With ropes or cordage, this will be done by analyzing the construction of the rope and the fiber(s) that the rope is constructed from. When analyzing tape, the analyst considers the composition of the backing and adhesive and also any special features like fiber and weave of the scrim (the cloth used in duct tape), any other fibers used in the tape to strengthen it, or special features. It should be noted that, especially with tape, there may be other trace evidence between the layers of tape, which would be from the location where the device was made or the tape applied. Therefore, if the tape can be delivered to the laboratory with the layers mostly intact, the analyst can look for any evidence between the layers.

Q: Should I submit spent bullets to the firearms unit even if I have no gun to compare them with?

A: Yes. There is information regarding the type of gun that can be gleaned from the rifling on the spent bullet. For an explanation of general rifling characteristics, go to: http://www.firearmsid.com/A_nogunid.htm





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