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How the FBI Handles Forensic Examinations

How the FBI Handles Forensic Examinations

Over the course of its existence, the FBI has set the gold standard for forensics.  What we’ve provided here is a guide for forensic science buffs on how the FBI conducts laboratory analysis and evidence collection, both for itself and for other law enforcement agencies.

How Crime Scenes Are Searched

Investigators of crime scenes, unfortunately, have to choose one of two search methods.  They can either slowly comb over the visible areas, preventing the evidence from being compromised, or they can conduct in-depth searches of concealed areas, ripping up furniture and pulling out drawers.  Regardless of method, there is no such thing as too much physical evidence.  Before a scene can be properly searched, a great deal of preparation is necessary.  This includes obtaining a search warrant and any other necessary paperwork, gathering proper equipment, and selecting personnel.  The investigators should also sketch out a plan for searching, including where and how to search, and what kind of evidence the search should focus on.  At the start of the search a preliminary survey is conducted.  The investigator walks through the crime scene, narrating his or her observations with audio, video, written notes, or a combination thereof.  Photographs are taken.  A search area is delineated.  Especially volatile or ephemeral physical evidence is protected.  At this point, a tentative analysis of the crime is developed.

After the preliminary survey, physical evidence is gathered.  Evidence in easily accessible areas is gathered first, with the investigators moving on to hidden areas.  They check to see if anything has been moved, intentionally or unintentionally, and whether or not the scene was contrived.  The investigators should keep a narrative, using a systematic method.  Photographs and sketches are used in conjunction with the narrative, which should detail date, time, location, weather, lighting conditions, personnel positions, the position of evidence, and anything that seems pertinent to the case.  Photography of the crime scene should occur as early as possible in the investigation, with a special emphasis on fragile areas.  Photographs should be well-documented, and each photo should be tagged with a location, date, and time.  Numerous heights and angles should be used.  Any object photographed should be photographed both with and without an object for scale.  All possible entrances and exits should be photographed.  In some cases, sketches can be used to supplement photographs.

A specific search pattern should be implemented.  This can be a grid, a spiral, or a strip.  All entrances and exits should be searched, and investigators should start with general searches, and then get more specific.  The evidence itself should be handled minimally, and evidence packages should be sealed at the scene.  Known standards should be obtained at the crime scene, such as a carpet that could provide fibers.  At the end, a final survey can be conducted to ensure that the search is complete, that all evidence is secured, and all equipment has been retrieved.  This is a good time to make sure hidden spots haven’t been overlooked.  The final survey site should be photographed.  If any experts need to be brought in to observe the crime scene, they should have seen it by now.  At this point, the crime scene can be released.

Types of Evidence the FBI Can Examine

  • Abrasive material used to sabotage machinery
  • Adhesives, caulks, and sealants can be compared by color and composition, but not by manufacture.
  • Anthropological evidence can be determined from bones.  This includes height, stature, race, sex, and any damage to bone.
  • Arson evidence can identify devices used to start fire and accelerants.
  • Audio can be scanned for authenticity.
  • Audio can be enhanced to reduce noise and improve clarity.
  • Audio recordings of two voices can be compared.
  • Audio signal analysis can be used to interpret non-voice sounds.
  • Damaged audio can be repaired.
  • Bank security dyes.
  • Building materials
  • Bullet jacket alloys can be analyzed, and manufacturer can be identified.
  • Bullet lead
  • Chemical analysis of unknown substances can be performed, but with no guarantee of complete identification.
  • Computer data, deleted or not
  • Computer source code
  • Passwords can be recovered and found.
  • Controlled substances
  • Controlled substance residues
  • Crime scene surveys and reconstructions can be created, and already finished surveys and reconstructions can be examined.
  • Encrypted documents can be analyzed and decoded, including drug deal records, gambling books, sharked loans, and documentation of money laundering and prostitution.
  • Nuclear and mitochondrial DNA can be analyzed, but it’s especially important for law enforcement to properly document, package, and preserve it.  This can include blood, dried or liquid blood on a person, blood on surfaces, blood in snow or water, bloodstains, semen, semen stains, semen samples taken by a doctor from sexual assault victims, oral swabs, saliva, urine, hair, tissues, bones, and teeth.
  • Consumer electronic devices like cell phones and GPS devices
  • Wiretapping devices
  • Data from other electronic devices and circuitry
  • Explosive devices
  • Explosive residues
  • The FBI disaster squad can assist with forensic services at disaster scenes.
  • Feathers
  • Firearms can be analyzed in multiple ways.  Manufacturer, model, condition of the firearm, pressure necessary to release the firing pin, and modifications.  Scratched off serial numbers can be restored.
  • Bullets can be matched to specific firearms.
  • Cartridge cases can be examined for manufacturer, caliber, and model, and can be matched to specific firearms.
  • Shot pellets, buckshot, and slugs can be matched to gauge and manufacturer.
  • Wadding components can be matched to gauge and manufacturer.
  • Unfired cartridges can be examined for gauge, and sometimes possess marks of value.
  • Gunshot residue from clothing can sometimes be matched to firearms.
  • Gun parts
  • Silencers
  • Glass can be analyzed for direction and force of fracture.
  • Gunshot residue from the hands of the firer
  • Hairs
  • Fibers can be matched to known fabrics
  • Photographs of people, places, and things can be matched to real-life people, places, and things
  • Dimensions of people, places, and things can be determined from photographs.
  • Photographs can be tested for source, age, location of photography, time and date of photography, authenticity, and manipulation.
  • Cameras
  • Videos
  • Automobiles in photos can be identified for make, model, and year.
  • Ink from writing can be compared to pens, and can be helpful in conjunction with handwriting analysis.
  • Latent prints from crime scenes
  • Photographs of latent prints
  • Fingerprints of an unknown deceased
  • Lubricants
  • Pieces of metal can be matched to other pieces and analyzed for identifying characteristics.  Metal can furthermore be analyzed for mechanical properties, chemical composition, and the way in which it was manufactured.  If the metal is broken, burned, heated, melted, or cut, the way in which it was broken can be found.
  • Watches, clocks, and timers
  • Lamp bulbs
  • Biological samples can be sent in and compared to the National Missing Persons Database.
  • Paint can be compared between tools and paint samples.  Paint chips from automobiles can be matched to make, model, and year of that automobile.
  • Pepper spray samples
  • Pharmaceuticals
  • Polymers
  • The laboratory can test for signs of product tampering.
  • Handwriting isn’t always linkable to a specific writer.  A limited amount of known writing, a lapse of time between two pieces of writing, lack of identifying characteristics, manipulation of handwriting, photocopying, or some combination of these can all prevent conclusive identification of handwriting.  Contrary to popular belief, personal traits cannot be linked to handwriting.
  • Altered or partially destroyed writing can sometimes be deciphered.
  • False signatures, whether done freehand, copied, or traced, can be readily detected.
  • Typewriting can sometimes be matched to a typewriter or individual typewriter parts.
  • Photocopied documents can on occasion be matched to a photocopier.
  • Torn paper can sometimes be matched along a common edge to another piece of torn paper.  Paper can also be examined for indented writing, and sometimes its manufacturer can be found.
  • Information on charred paper can sometimes be deciphered.
  • The age of a document can be determined by printing, typewriting, and type of paper.
  • Carbon paper can be examined for text.
  • A rubber stamp, embossing, or printmaking apparatus can sometimes be paired to a mark that it’s made.
  • Bank robbery or anonymous notes can be compared to other bank robbery or anonymous notes.
  • Plastic bags can sometimes be matched to the roll or box they were packaged in.
  • Ropes and cords
  • Insulation
  • Serial numbers
  • Photographs or casts of shoe prints and tire prints
  • Crime scene photographs
  • Photographs taken in snow can be somewhat difficult to photograph and analyze.  The FBI provides guidelines for photographing in snow.
  • Electrostatic, gelatin, or adhesive lifts of impressions.
  • Soil
  • Tape
  • Toolmarks can frequently be matched to tools thanks to microscopic indicators.
  • Toxicology reports can reveal volatile compounds, heavy metals, pharmaceuticals, and poisons.
  • Wood
  • Video evidence can be clarified and enhanced, formatted, modified, or tested for authenticity.
  • Damaged video can be repaired.
  • Video stills can be processed into photo images for analysis.