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Scientific evidence is information that has been developed
through a process known as the "scientific method"
-- meaning that the information is considered valid because it
has been tested and shown to accurately describe what it
purports to describe. Typically, scientific evidence has been
published in journals, tested by other scientists and
generally accepted as valid within the relevant scientific
community. Common examples of scientific evidence include DNA
analyses, hair and fiber comparisons, fingerprints and voice
identification evidence. Because scientific evidence is by
definition beyond the realm of judges' and jurors' everyday
experiences, the prosecution and the defense use qualified
expert witnesses to introduce scientific evidence into the
courtroom.
There are, of course,
rules about when and how scientific evidence may be used in
court. If a scientific theory is well established, testimony
from a qualified expert witness based on that theory is
usually admissible at trial, without additional expert
testimony regarding the reliability of the evidence. For
example, an expert is seldom necessary to convince a judge of
the validity of fingerprint analysis or radar speed testing
devices. However, as novel scientific theories emerge, experts
must convince judges that information based on these new ideas
is reliable and therefore appropriate for consideration by the
judge or jury.
To establish the
reliability of scientific evidence, the party seeking to
introduce the evidence ordinarily schedules a
"mini-trial" in which an expert testifies and
explains the scientific methodology involved. For example, to
use DNA evidence for the purpose of identifying a suspect (by
comparing samples taken from the suspect with samples found at
the crime scene), some judges still require the prosecutor to
establish the reliability of that evidence in a mini-trial. If
the judge is then convinced of its reliability, DNA evidence
can be used in that case. Most courts, however, now accept DNA
evidence as reliable and do not require a foundation (the
function of the mini-trial) for its use.
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