Michigan residents who are charged with a criminal offense face the possibility of going to trial. In fact, it's their right to take a matter to trial if they so wish. At trial, it is the prosecution that bears the burden of proof. This means that a criminal defense needs to only raise doubt as to the defendant's guilt and poke holes in the prosecution's arguments. In other words, innocence does not have to be proven beyond a reasonable doubt, guilt does.
One way to challenge a prosecution's claims is to aggressively attack the chain of custody. Chain of custody refers to the documentation, care, and handling of evidence from when it is first seized to the time that it is presented in court. When the chain of custody is not sufficiently established, then how can one know that the evidence has not been tampered with or contaminated? This is the main question in chain of custody issues. This often comes up in cases where drug or alcohol tests are being utilized by the prosecution, but chain of custody can also be raised with regard to other physical evidence as well.
Let us look at an example. If an individual is facing allegations of driving while intoxicated and caused a fatal wreck, then the police may draw their blood for toxicology purposes. When the matter goes to trial, if the prosecution does not have the person who took the blood sample testify as to the process and their handling of the sample, then the initial link in the chain of custody is not established and that evidence may be deemed inadmissible.
Mislabeling, mishandling, and witnesses who are unavailable to testify can all cause chain of custody issues for the prosecution. However, if an objection is not made by the defendant in these instances, then the evidence is likely to be admitted. Therefore, those facing criminal charges may want to ensure they have someone on their side who knows the evidentiary rules and can utilize them for the defendant's advantage.
Source: FindLaw, "'How to Suppress Evidence," accessed on June 11, 2016