In a criminal prosecution, the state or federal government will often depend on a prosecution witness to prove its case. A prosecution witness is often a law enforcement officer, but may be a civilian as well. Civilian witnesses may include a victim of the crime, an expert witness, a confidential informant, or a bystander who witnessed the crime when it happened.
During a criminal trial, the prosecution must present its case to the judge or jury and convince them that the defendant committed the crime. Evidence may be admitted as part of the prosecution's case. Evidence may be in the form of documents, tangible evidence, or testimony from witnesses.
A law enforcement officer is almost always included as a prosecution witness. The law enforcement officer may testify to what information was gathered during the investigation of the crime or what was personally observed by the officer. In addition, testimony may be offered regarding any statements the defendant made to the officer after the arrest was made.
Confidential informants are also considered a prosecution witness. In many cases involving drug trafficking, a confidential informant is used to provide information or even to make purchases on the part of law enforcement from suspected traffickers. If the case goes to trial, then the confidential informant will need to testify against the defendant.
The victim of a crime, as well as bystanders, often make excellent prosecution witnesses. As a rule, their testimony is considered very credible and may be the most detailed evidence available. A victim often testifies at a sentencing hearing as well in order to express how the crime has affected him or her from an emotional standpoint.
Criminal trials frequently use scientific evidence in order to convict a defendant. DNA results, blood splatter results, ballistics, and fingerprint analysis are just a few of the possible types of scientific evidence admitted in criminal trials. In order for a jury to understand the process of analyzing and reaching conclusions based on scientific evidence, the prosecution may take testimony from an expert witness. This type of prosecution witness is responsible for explaining the results of highly scientific tests in a manner that allows the jury to understand the implications of the results.
Although a person may be listed as a witness for the prosecution, the defendant will also be given the opportunity to question the witness. The defendant may be able to establish that the witness is biased or that the testimony he or she gave was inconsistent. In some cases, a prosecution witness actually ends up being more beneficial to the defense.