Paint can be important evidence in criminal investigations. This lesson will review the significance of paint as forensic evidence and discuss how it can be collected and preserved for forensic examination.

Paint as Forensic Evidence

David is on his daily ten-mile bike ride. It's Sunday, and there is not much traffic to speak of, so David startles slightly when he hears a car approaching behind him. The car appears to be speeding, and as it attempts to pass David, the vehicle clips David's back tire and sends him flying over the handle bars and onto the road. The vehicle takes off without stopping. Another car pulls up a few minutes later and calls 9-1-1.

As rescue workers rush David to the hospital in critical condition, law enforcement arrives and starts the investigation. One of the officers notices white paint on David's blue bicycle frame and assumes the paint belongs to the vehicle that hit him. The forensics team is called in to collect the paint evidence and an intensive investigation is launched.

When most of us think about paint, we think about putting colors on our walls or choosing a paint color for our vehicles. However, paint can be powerful forensic evidence, or evidence that can be utilized to solve crimes. Like glass, fibers, and hair, paint is considered to be trace evidence. In other words, it is evidence that is transferred from a main source to the scene of a crime. In our opening example, the paint transferred from the car to David's bicycle is evidence, giving investigators a good immediate clue as to the color of the car they're looking for.

Paint trace evidence is especially relevant in cases where automobiles are involved, but it can also be useful in other cases. For example, a burglar using a crow bar may leave paint markings behind on the frame of a door or window which can be collected and analyzed as evidence. This can tell investigators details about the color of the crow bar that was used, so they can have a better idea as to what type of crow bar was used to commit the crime. Paint evidence can also tell us what type of paint investigators need to be looking for. The characteristics of nail polish, for example, are very different than those of paint used on automobiles or house paint.

Collecting Paint Evidence

In order to collect and preserve paint evidence, it is important to start with securing the scene of the crime. Prior to the collection of a paint sample, the area containing the sample should be photographed without disrupting the evidence. Any disruption to the crime scene area could potentially contaminate the paint evidence. Investigators can then proceed to collect the paint sample, typically by carefully scraping or peeling the paint from the surface area where it was located. Tools such as tweezers might be used during the collection process.

Until the paint evidence can be forensically examined, it should be carefully preserved so that it remains unaltered while it is transferred from the crime scene to the laboratory. All paint samples should be kept in separate containers. If paint evidence is found on clothing, it should not be removed. Rather, the clothing should be rolled up in paper and sent to the lab.

Once in the lab, the examination will begin. Investigators will look for several things, such as the edges of the paint sample, and whether or not there are multiple layers of paint present beyond the surface layer. In our example story, this could help police determine if the culprit's car is newer or older, as a paint chip from a car that has been painted several times over the years is likely to have multiple paint layers.

Analyzing Paint Evidence

The analysis of paint evidence takes place in a forensics laboratory with specialized equipment. The following are some methods by which paint can be forensically analyzed:

  • Microscopic examination - during forensic investigations of paint chips, microscopic exams are almost always performed. Under a microscope, and more specifically a stereoscopic microscope, investigators can get enhanced details from paint samples that would otherwise go unnoticed, such as characteristics that might be indicative of a particular paint manufacturer.
  • Pyrolysis gas chromatography - this process involves applying heat and gas to analyze paint in great detail. Pyrolysis can help to differentiate paints of the same color. This can be useful in narrowing down the actual make and model of a vehicle; for example, by isolating a particular paint color used by the manufacturer.
  • Infrared spectrophotometry - this method utilizes infrared lighting to analyze paint fragments. The process works by shining infrared lighting through a paint sample and measuring how the paint absorbs the light source.

The forensic analysis of paint can provide important clues in a criminal investigation. In the case of a hit and run victim, paint that is found on the victim's bike can give us insight into the vehicle involved in the crime.

Lesson Summary

Paint can be a type of forensic evidence, or evidence that can be utilized to solve a crime. Paint chips or remnants can reveal a significant amount of information during forensic investigations. Paint that is located at a crime scene is referred to as trace evidence, because it has been transferred from a main source to the scene of a crime. Paint evidence is especially useful in the investigation of crimes involving automobiles, but can be useful in other investigations as well.

After a crime scene is secured, forensic investigators need to proceed and collect the paint samples carefully. This is usually done by scraping or peeling off the paint evidence. If paint is found on clothing, the clothing is preserved in paper.

Paint evidence can help investigators determine the type and color of the paint and whether or not multiple layers and/or colors of paint are contained in the sample. By narrowing down paint details in a hit and run crime scene, the manufacturer of the paint can be determined and ultimately lead investigators to identify the type of vehicle that was involved.

Once the evidence has been carefully preserved, it is sent to the lab for forensic analysis. The analysis of paint evidence can be done using a variety of techniques including through the use of microscopic examination, investigators can get enhanced details, particularly through stereoscopic microscopes, as well as pyrolysis gas chromatography, in which heat and gas are applied to a paint sample, allowing for detailed analysis. Forensic scientists can also use infrared spectrophotometry, in which they shine infrared lighting through a paint sample and measure how the paint absorbs the light source.