Processing Vehicles for Unique Types of Evidence
Written by Christopher D. Duncan   

An excerpt from Processing Vehicles Used in Violent Crimes for Forensic Evidence

This article appears in the November-December 2021 issue of Evidence Technology Magazine.
You can view that full issue here.

CRIME SCENE INVESTIGATORS MUST BE PREPARED to recover almost any kind of object or process for any kind of evidence at crime scenes. Vehicles are no different than a crime scene in the field, but they do have the benefit of being processed in a more controlled environment. Investigators should take advantage of this opportunity.

One type of vehicle that will frequently enter the facility will be one from a hit-and-run investigation. Typically, accident or crash investigation units handle hit-and-run investigations, also known as Fail to Stop and Render Aid (FSRA) or Fail to Stop and Give Information (FSGI). However, not every agency will have an investigator specifically assigned to process vehicles involved in a hit-and-run investigation or the hit-and-run incident was not an “accident,” but rather it was intentional, which changes the agency’s investigative division’s responsibility. There are a couple of common requests made when processing hit-and-run vehicles, and they revolve around the need to identify what came into contact with the said car, whether it was another car, object, or a human being.

When two vehicles impact each other, there is generally an exchange of paint between the two vehicles. Edmund Locard’s “Theory of Exchange,” which states “Every contact leaves a trace,” dictates that there will be a transfer of material between the two contacting surfaces.

Recovering the paint or debris left behind is the job of the evidence technician. Removing debris and paint from a vehicle is typically done by scraping the material with a sterile surgical blade or a knife that has been thoroughly wiped down with isopropyl alcohol. Paint transfers from minor impacts may not come off as easily with just a surgical blade or scalpel. However, this does not preclude the investigator from recover­ing such evidence. More severe impacts likely will cause a vehicle’s paint to crack and is much easier to scrape off.

Whichever tool is chosen to scrape the material or unknown paint from the vehicle, the unknown paint or debris is scraped into an evidence envelope or a druggist-fold envelope for collection. Paint chips have a tendency to chip away at odd angles. Therefore, investigators should be cognizant of that possibility and keep the scrap­ing action or force downward, so that all material is going to be pushed or fall into the evidence envelope that is held just below the area being scraped. Eventually, the envelope will be sealed and marked with the case information. If the unknown paint transfer was scraped from the examined vehicle’s own painted surface, investigators should also collect a known paint sample of the vehicle being examined and from the same surface, but away from the damaged portion of the automobile. The collected sample should be approxi­mately the size of a United States quarter. As far as the unknown paint or debris collected, it is recommended to collect as much of the foreign material as possible. One does not need to stuff an evidence envelope full of material, but no one is going to complain if “too much” evidence is collected.

Another type of hit-and-run accident that sadly is all too common are vehicle-pedestrian or vehicle-bicycle hit-and-run crashes. If a suspect vehicle is brought into an examination facility, it is up to the evidence technician to find traces of the victim on the vehicle. Depending on where the impact was on the vehicle, it may be necessary to have the vehicle lifted on the car lift and to look on the vehicle’s undercarriage for trace fibers, DNA, or other pieces of evidence. Fiber evidence can be collected and placed into a druggist fold or glassine envelope. A suspect may wash the exterior of the vehicle but may forget to do the unseen areas—so be sure to look for evidence underneath the vehicle, stuck in the radiator’s front cooling fins, or behind the grill or other trim pieces (Figure 1). If the vehicle has been cleaned by the suspect, what remains may be just a single fiber or two. If the victim was run over, the undercarriage of a vehicle should be thoroughly examined and special attention paid to any swipe marks visible through the grime commonly found on the undersides of vehicles. Even if no physical evidence is located underneath a vehicle, any swipe marks observed on the vehicle should be photographed and fully documented. It may be circumstantial evidence, but the evidence is evidence. Blood, tissue, and other serological evidence can be collected through the swabbing technique detailed in Chapter 7.

Figure 1. Evidence from a hit-and-run can be extremely small, especially if the vehicle belongs to the suspect and it has been washed. This photograph shows a single hair from a hit-and-run victim hanging from underneath one of the vehicle's wheel wells.

Another common task requested during crash investigations is determining the iden­tity of the driver or the positions of passengers at the time of a collision. Investigations should search for and recover any bloodstains found inside the vehicle. If bloodstains, hair, or tissue are not found, then the investigator should collect touch-DNA swabbing samples from the vehicle controls, seatbelt straps, and any deployed airbags. Airbags generally deploy with such force that bloodstains or other body fluids are commonly found. The advantage of recovering DNA from airbags is that it places a time stamp on when the indi­vidual came into contact with the airbag.

In the course of vehicle crashes, pieces of a vehicle may be left behind at the scene of a crime. Any vehicle glass, plastic, or other parts left behind at the crime scene should be collected. The damaged pieces hold a great deal of information, including the make and date of manufacture for a vehicle. Furthermore, if just a portion of something is left behind at the scene, then it is possible to make a fracture match between the two pieces. Consequently, when a suspect’s vehicle arrives at a vehicle examination facility, which has damaged trim and/or glass, these items should be examined closely. Vehicle examiners should remove damaged parts of the vehicle so that any potential fracture matches can be made between the debris left behind at the crime scene and the remaining pieces left on the vehicle (Figure 2).

Figure 2. In the course of committing an aggravated robbery, the suspect's vehicle was damaged, leaving a piece of the taillight assembly behind at the crime scene. When the vehicle was located, the damaged taillight was removed and a fracture match was made between the portion of the light recovered from the vehicle and the pieces recovered at the crime scene.

Car parts and window glass all have part numbers stamped or printed on them somewhere. Therefore, even if the car was repaired, one may be able to compare part numbers or date codes and determine if the vehicle had been repaired. For example, if a taillight assembly was damaged at a scene, but repaired by the suspect prior to the vehicle being seized, the examiner may be able to show that the vehicle’s model year and the repaired part’s manufacturing year are different (Figure 3).

Figure 3. Most every part of a vehicle will possess some sort of part code and larger parts of the vehicle will possess additional information, like make, model, and date of manufacture. Comparing this information might give an indication if any repairs had been made to the vehicle at some point.

Because of how vehicles are manufactured, parts are generally date coded within 30 days of the vehicle’s assembly date. Some of the manufactured dates will not be as clear as a numbered date but will be printed in a code. This is especially true with car window glass. Date codes on windows can be a unique arrangement of letters, numbers, and even through small dots placed next to letters on the information printed on each window (Figure 4). There is no standard between manufacturers as to the date coding of window glass or vehicle parts. Some of this coded information may be deciphered through an internet search, but others might require contacting the manufacturer for decoding of the information.

Figure 4. Every vehicle's original glass window will have a coded manufacturer's date and other information printed on it. This information can possibly tell an examiner if the window is a replacement or if it is original to the vehicle. The coding on window glass is unique in that the combination of numbers and the little dots next to the text identify the manufactured date, such as the small dot above the letter "A" in the word "TEMPALEX" found in this photograph.

Burned vehicles, whether accidental or intentional, present another unique type of investigation that requires a whole new set of investigative skills. Arson investigators are commonly cross-trained in fire and police investigations and many times will take the lead during the examination of burned vehicles. They will look at a burned vehicle and attempt to deter­mine the cause and origin of the fire. Fire science and the determination of the cause and origins of fire are well beyond the scope of this book. However, there are a few tasks an evi­dence technician can do to assist arson investigators. One is to positively identify the vehicle through VIN plates remaining on the vehicle (Figure 5).

Figure 5. Arson investigators can determine the cause and origin of a fire, but vehicle examiners can help positively identify the vehicle, especially vehicles that were completely decimated by fire and reduced to bare metal.

As with every investigation, the photographer should thoroughly document the vehicle with photographs, especially in the area where the most fire damage occurred. The origin of the fire is generally the location where the most fire damage is found because the fire had more time to burn. The cause may be found by locating the source of ignition or telltale signs of an accelerant being used in the car. Many accidental fires will start in the engine compartment and spread from there. If a fire started anywhere else, the arson investigator will look carefully for any signs that an accelerant was used, such as a gas can or a burn trail leading away from the vehicle at the recovery scene. The crime scene investigator or evidence technician should follow along with the arson investigator and photograph all key aspects of the investigation.

The interior of severely burned vehicles will have to be sifted through very carefully to look for evidence and even for deceased bodies. One must be cognizant of what fire can do to objects and to human bodies. Fire will burn off much evidence, but others will take on different forms. For example, plastic gas cans may melt and be found as charred-red disks of plastic instead of their original container shape. Bodies can be burned away simi­larly and extremely hot fires can turn a body into hundreds of calcined bone fragments that are extremely delicate and must be recovered with extreme care. Having a forensic anthropologist would be extremely helpful when a burned body is located. They can be enormously helpful in recognizing osseous matter and may even be able to identify bone trauma that might give an indication as to the fire victim’s cause of death. Investigating crimes and especially crimes involving fire is definitely a team effort and any help offered to an evidence technician should be welcomed.

Searching through a burned vehicle is done by sifting through layers of debris found in the car. This can be done by using a small brush and a dustpan and by removing debris from the vehicle a little at a time. In this way, one will be less likely to miss a small piece of evidence, like a melted, fired bullet. Do not forget to photograph as the search progresses through the various layers of debris (Figure 6).


Figure 6. Extremely hot fires can reduce a body to calcined bone, which is extremely fragile and needs to be recovered with extreme care. One needs to search through a vehicles contents carefully, by sifting through the vehicle and moving fron the top layers of debris down.

Package any evidence, taking special note of exactly where each item was found. The arson investigator will likely take care, custody, and control of any arson evidence, while the forensic anthropologist will take responsibility for any human remains. Everything else of value will be the responsibility of the evidence technician.

About the Author
Christopher (Chris) D. Duncan graduated from George Mason University with a BA in History and earned his MA in Criminology from the University of Houston-Clear Lake. He is a retired senior police officer with the Houston Police Department and was previously an active member of the International Association for Identification. Duncan has written several articles on forensic evidence collection and documentation and has more than 1,500 hours of training specific to the documentation, collection, and the processing of physical evidence, having worked 20 of his 29 years in law enforcement as a crime scene investigator. Prior to his days in the crime scene unit, he was assigned as a patrol officer and a gang task force officer. Duncan now teaches Criminal Investigation and Law Enforcement classes at Klein Collins High School in Texas.

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