Scientific and Forensic Evidence
There are many types of evidence that are commonly used at trial. Scientific and forensic types of evidence can be extremely helpful in proving your case, but there are rules and standards that these types of evidence must meet before they can be submitted during a trial.
You may be wondering what on earth scientific evidence could mean in regards to a trial. In general, scientific evidence is based off of knowledge that has been developed by using the scientific method. This means that the basis for the evidence has been hypothesized and tested and is generally accepted within the scientific community. This could mean that the theory on which the scientific evidence is based has been published in scientific journals and has been subjected to peer review within the scientific community.
Generally, many types of forensic evidence are often considered scientific evidence, like DNA matching, fingerprint identification, and hair/fiber evidence. The methods used to develop these types of evidence are generally beyond the scope of knowledge that judges and juries possess and are therefore normally introduced as scientific evidence.
However, this is not to say that scientific evidence cannot be excluded from a courtroom or trial. There are often many steps that must be taken before a piece of scientific evidence can be put forth in a courtroom as factual evidence. In general, a scientific theory must have established itself in the scientific community and become generally accepted as the truth before it will be asserted as evidence at trial.
For example, because it has been around for so long and because it has proven to be reliable, evidence regarding fingerprint matching is generally admissible as forensic evidence in trial. In addition, things like radar and laser speed guns are generally accepted as being a valid method to tell the speed of a car at a given time and can be admitted as evidence. But keep in mind that there will often be new types of scientific evidence that parties will attempt to submit at trial - science that may not have a solid foundation within the scientific community.
If one side of a trial wishes to submit scientific evidence that is not yet generally accepted within the scientific community, it often happens that the court orders a mini-trial to be held in order to determine the validity of the scientific theory on which the evidence is based. As an example, DNA evidence had to go through many mini-trials before it became generally accepted as valid evidence at trail.
In the future, we may see more mini-trials as more types of forensic evidence are introduced in court. As another example, many scientists are currently working on using functional Magnetic Resonance Imaging (fMRI) as a new type of lie detection machine (this works by imaging, in real time, the flow of blood around the brain). If, during a mini-trial, a judge can be convinced that a new, as-of-yet unproven, type of scientific evidence should be introduced at trial, then the judge will allow it to be presented.