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What is a Prosecution Witness?

A prosecution witness is an individual called upon by the government or state in a criminal trial to testify against the defendant. Their role is to provide evidence that supports the prosecution's case, aiming to establish the defendant's guilt. These witnesses can range from eyewitnesses and victims to experts and law enforcement officers. Their testimony is a crucial element in the prosecution's effort to prove the charges beyond a reasonable doubt.

According to the Bureau of Justice Statistics, witnesses participate in a significant portion of criminal cases, with their testimonies often being pivotal for the outcome. For instance, in felony cases in large urban counties, about 90% of convictions are the result of plea bargains, where witness testimonies may influence the decision to plead guilty. In trials, the credibility and reliability of prosecution witnesses can be the linchpin of the case, underscoring their importance in the judicial process.

Renee Booker
Renee Booker

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.

The prosecution often depends on a key witness to help make its case.
The prosecution often depends on a key witness to help make its case.

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.

Blood splatter can be used as evidence.
Blood splatter can be used as evidence.

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.

A witness may be compelled to testify even if he or she does not wish to.
A witness may be compelled to testify even if he or she does not wish to.

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.

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Discussion Comments


@Vincenzo-- I agree that expert opinion is not always very important or effective. The jury might have trouble understanding the scientific information and the jury could also have doubts about the expertise of the scientist.

Although the prosecutor will bring a credible expert on stand, let's keep in mind that defense can question the witness as well. There are times when the defendant ends up benefiting from the prosecution's expert witness as the article said. An expert witness is not there to prove the prosecution right, he or she is there to relay scientific evidence and data truthfully. And that data can actually benefit either side.


@ZipLine-- If the prosecution witness is a law enforcement officer, I don't think that's possible. I suppose a civilian may refuse to testify but if they have agreed to it, why would they change their mind?

Sometimes a party to a criminal case may try to influence or even threaten a witness to change their testament. Or the witness may be pressured to not testify altogether. But the law provides protection against such threats with programs like the witness protection program.

Moreover, if it is determined that the defendant engaged in this type of behavior, it can cause the judge to rule against the defendant simply because of this. Threatening witnesses or meddling with evidence are very serious issues and the court will not take them lightly.


Do prosecution witnesses ever back off and refuse to give testimony?


@Terrificli -- having scientific evidence is one thing. Convincing a jury it is credible is quite another. A scientist who doesn't come off well to a jury may, in fact, help a defendant's case. This is particularly true in instances when a witness is relaying highly complex testimony that isn't explained well to a jury.

In other words, explaining what evidence means is as important as having good evidence to present. To that end, scientists must take pains to make sure they can address typical folks and explain complex concepts in terms that jurors can grasp.


Scientists and other professionals are increasingly important in criminal cases. Take the relatively new field of DNA analysis. A scientist who can, through DNA analysis, put a defendant at the scene of the crime can be particularly damaging to a criminal defendant's case. That is particularly true in the case of rape cases.

Once a scientist wielding DNA evidence convinces a jury of a defendant's guilt, the prosecution generally wins.

The importance of these witnesses cannot be understated because such scientific testimony was simply not available until recently. Advances such as fingerprint analysis and DNA evidence have gone a long way toward making sure justice is done.

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    • The prosecution often depends on a key witness to help make its case.
      By: Junial Enterprises
      The prosecution often depends on a key witness to help make its case.
    • Blood splatter can be used as evidence.
      By: mizina
      Blood splatter can be used as evidence.
    • A witness may be compelled to testify even if he or she does not wish to.
      By: TAGSTOCK2
      A witness may be compelled to testify even if he or she does not wish to.