A witness for the prosecution is a witness who is brought into the court in order to provide testimony which supports the prosecution’s overall case. A witness for the prosecution, thus, would likely provide testimony affirming that the defendant did whatever action he or she is being put on trial for, for example, or otherwise would produce some form of statement which helps to push the jury in favor of the prosecution’s argument.
Because a witness for the prosecution will often be providing testimony which is ultimately critical to the prosecution’s overall case, the prosecution will likely help to establish a witness statement for a witness for the prosecution. Such a witness statement would function as a summary of the facts and evidence which the witness is going to provide in testimony.
Sometimes, a witness statement may actually be all that is necessary for the witness’s evidence to be entered into the trial, as a full out questioning of the witness for the prosecution may be deemed unnecessary in light of the witness statement. In general, however, a witness statement is less often used within the courts of the United States of America, as the deposition and questioning process is much more often used.
The defense of a trial would focus on discrediting, in some fashion, any important witness for the prosecution, in order to take the weight off the testimony given by such a witness for the prosecution. For example, the defense would attempt to prove that it is possible that a witness for the prosecution did not see the things which he or she believes that he or she saw, in order to disprove the testimony of the witness for the prosecution, and thus add to the defense’s overall case.