What Can Go Wrong With DNA Evidence?

If there's apparent DNA "proof" being used against you, part of your defense should include an investigation into whether accepted standards were followed in collecting and processing the DNA evidence.

Use These Stringent Standards to Your Advantage

Here's the truth about DNA—it doesn't paint a complete picture.

There are many variables that make DNA strong and persuasive evidence, which some think of as the gold standard. On the other hand, there's a wealth of potential obstacles that can lead to DNA becoming contaminated or blemished.

In defending yourself against these life-ruining allegations, you should distrust DNA evidence against you. Understanding the steps involved in validating these samples is crucial to your cause.

Before we explain some of these best practices, keep in mind that we’re only presenting examples, and really this only scratches the surface. The guidelines referenced here come from "The Biological Evidence Preservation Handbook" published by the National Institute of Justice.

Best Practices for Packaging in Containers

First, it's suggested that paper bags, manila envelopes, and cardboard boxes are used for biological evidence. Really, anything with porous materials will do. It's then recommended that for extra padding in the evidence container, butcher or art paper should be used for wrapping.

The evidence container must be sealed to prevent cross-transfer, loss, contamination, or deleterious change.

Lastly, sealing must be done to cause apparent damage or change in appearance if it's opened. This is done as a security measure.

Best Practices for Packaging Items

First and foremost, everything should be separately bagged to avoid cross-contamination.

In the case of wet evidence that you can't dry, after placing it into the requisite container (discussed above), it must be placed in a fridge. The temperature of this fridge must be between 2 °C to 8 °C (or, 35 °F to 46 °F).

The evidence also can't be placed in any spot with access to direct sunlight until it can be dried or submitted to the lab.

All pieces of DNA evidence must have their integrity upheld through the documentation of the packaging—meaning seals, tags, labels, and markings used by all involved must be preserved.

When sealing the packages, staples aren't an ideal practice. Instead, each package of evidence must be sealed with tape, heat seals, or gum seals. The sealer's identification or initials and the date must be marked across the seal.

As far as packaging goes, this isn't even the whole picture. It's an incredibly extensive process with complicated documentation procedures.

Why Are Practices So Stringent?

These guidelines are so strict and rigorous because there are collection methods that promote the growth of bacteria and mold on the evidence. There are also the pressing needs to prevent both cross-contamination and evidence tampering.

Discrediting This Evidence

The primary purpose of showing you these rules is to give you a direct lens into how stringent DNA evidence collection can and should be.

In crafting your defense, you want to do what you can to ensure these standards were meticulously followed. It's up to law enforcement to do their job correctly for evidence to be valid.

You don't deserve to have your name on the Child Abuse Central Index after an officer or lab technician failed to seal packaging correctly or didn't take the time to document appropriately.

By way of another example, if the DNA evidence against you is kept in a room by a police department where all employees can access a short-term storage solution.

This may bring the integrity of the sample into question, as relating to the chain of custody. It can also lead to the commingling or cross-contamination of the evidence.

If anyone but the submitting and property officers have access to the evidence, it may be susceptible to being discredited.


All is not lost if DNA evidence is used against you. There are plenty of things that can go wrong. We hope that this has given you some confidence in your chances to overcome these accusations.

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