Paint, glass and soil sample collection

Document the methods for collecting and preserving samples of paint, glass, and soil. What is the responsibility of the field examiner? What can the criminalist show in comparison, and what is needed for comparison?

The proper collection of evidence can literally make or break a case. OJ might be living out two life terms right now if evidence had been properly collected, documented, and of course brought to the station or lab instead of sitting in a detective’s car overnight. There are ways of collecting certain pieces of evidence and one must be careful to do the job correctly or the evidence you spent so long collecting could turn out to be unusable. The following will note the proper collection for:

Paint: Paint evidence is most often found at hit-and-run scenes. This may be in the form of transfer or paint chips. When paint chips are discovered at a scene they must be carefully collected in order to keep the chip intact. If tweezers are not available, a clean piece of paper may be used. If using paper, ensure that a druggist fold is used to maintain integrity. Be sure to properly document the papers. If using tweezers, a plastic container or vial is perfect. 

If the paint evidence is transfer, do not attempt to remove the paint from clothing or a bicycle. Package the items to the best of your ability and bring the entire thing for testing. When you have a suspect vehicle, collect your sample from an undamaged part of the car that is close to the area that struck. Collecting a sample from another part of the car all together might not result in a match because another area may have faded or even been replaced and repainted at some point in the car’s life.

When collecting a sample, a new disposable scalpel must be used each time and one should get a quarter-inch sample that goes all the way down to the bare metal, package each sample individually and note where on the vehicle it was taken from.

Glass: A careful examination of both your suspect and the crime scene is essential to finding and documenting glass evidence.  How many times have we broken a glass on the kitchen floor and thought we found every piece until we step on the one piece we missed because we didn’t see it? That one painful piece could have won us the case. There are several different types of glass and just as many scenarios where it should be collected. Broken pieces of a cars headlight at a hit-and-run, window glass found on a suspect, or painted or colored glass that might have been used as a weapon. If possible, collect at least one quarter inch of glass from the source, even if you don’t have a suspect now, you might find one down the road and there is still a chance that a match could be made. When collecting from the source, notate if the collection is interior or exterior glass such as the case in a double pane window. If it is not possible to know if the sample is interior or exterior an examination of the glass should show a certain amount of dirt, pain or even pollen on one side of the glass.  Be sure to package glass fragments in a solid container so that it does not break any further. Should you have a suspect, that person’s clothing and shoes should all be wrapped individually in paper wrappers and transported to the lab.

Soil: When a civilian thinks of soil they think of dirt. When an investigator thinks of soil, they consider rocks, leaves, animal scat, ashes, rocks and vegetation to be included in the collection of the dirt. The collection of any or all of these material is valuable as it shows it to be present in a particular location and differentiates it from other locations. Evidence such as this that is found on a suspects shoes or clothing may be able to prove that they were in said location instead of at their aunt’s mother’s best friend’s house or anywhere except admitting to being at the scene. When collection soil samples from a crime scene the first samples of course should be at the active site. Other samples must be taken however at set intervals within a 100- yard area to better prove the suspect was present in the immediate area. For example, if a victim was found beside a road and proper soil collection was done then we as investigators would think to pick up a half-stepped on piece of dog poop. A week from now, we may conduct a search on a suspect’s home and find a pair of boots with the other half of the dog poop on them. Having the original sample may enable a criminalist to place the suspect in the location of the scene.

When collecting a sample in most cases it is not necessary to dig down into the soil and a couple of tablespoons is a sufficient sample size to be tested. Place the soil in a plastic container and properly mark the container. If soil is found on a known suspect, the clothing and shoes must be collected into paper bags and marked for evidence. If collecting dirt from a suspect or victim’s vehicle, collect samples from inside the wheel wells of the vehicle as layers tend to build up in that area. Under the fenders and frames of the vehicle is another place to collect dirt evidence when searching a vehicle.