A "government witness" is someone who gives evidence or testimony in a legal case on behalf of the government. They are usually called upon to provide information that supports the government's side of the case.
Catch up on the charges and the key government witness. (newsday.com)
A good cross examination can bring out the «other side» of the story to show why a certain government witness should not be believed. (jsvlawyer.com)
«I love him as a brother,» the star government witness in the obstruction - of - justice trial of state Sen. John Sampson said Thursday as he took the stand to bury his friend... (nypost.com)