Evidence testing isn’t always handled properly in criminal cases

Many different forms of evidence can arise when you are facing criminal charges. Some evidence may be subject to laboratory tests that must involve well-controlled collection, testing, and chain-of-custody protocols. Without these in place, there is a chance that evidence will be improperly tested.

Whether the evidence is DNA, drugs or something else, digging deep into everything, from how it was collected to what happened during the testing, is imperative in criminal cases. Even the smallest contamination of the sample can invalidate a key piece of the prosecution’s evidence against a defendant.

Collection of evidence

When the evidence needs to be tested, it has to be carefully collected. At a crime scene, the person who is gathering evidence needs to use clean collection kits and supplies. They need to wear gloves during the process. Ensuring that only the applicable items are collected is imperative.

Once the evidence is collected, it needs to be properly labeled so that it can be tied to the correct case. If a police officer accidentally transposed digits on a case number or got a name or location wrong, it could be a game-changer for the viability of a criminal case. The defense could credibly argue that the prosecution can’t be certain to which case the sample belongs.


Most police departments will send the evidence to a crime lab for testing. Because this involves them handing the actual evidence to another party, there is a need to have a controlled chain-of-custody. The more people who handle the evidence, the more likely it is that something will go amiss.

Each person who handles the evidence should be notated in the chain-of-custody record. What they did with the evidence should also be noted. For example, if a detective checked out a stash of drugs to take a picture or a crime lab technician tested the evidence to determine its type, that should be noted.

Testing protocol

Lab testing must be conducted in a very controlled manner. This is especially important with DNA testing. If a person sneezes or if moisture collects in the sample bag, the sample might be invalidated. Improper handling during testing can lead to incorrect results in all types of testing. Throughout the country, there have been cases that had to be thrown out because the evidence was adulterated during the testing process. In 2018, defense attorneys in another state had to ask that more than 11,000 cases be dropped due to improper handling at the state’s drug testing lab.