The upcoming trial of a former governor and his wife on federal corruption charges highlights a common and sometimes controversial tactic used by prosecutors: testimony from witnesses who have been offered immunity from prosecution themselves.

Although the case is not being brought in the state of New Jersey, the issue of immune witness testimony is relevant to many federal crimes and state criminal prosecutions in every state. Prosecutors in trials across the country often rely on such testimony when seeking to establish the existence of alleged conspiracies or other crimes in which the intent of the defendants is something that the government must prove.

In the case at hand, the government’s contention is that the former governor and his wife accepted gifts and other items with a value of at least $165,000 from a business owner in exchange for helping him to promote his business; an exchange which the prosecution alleges was made with corrupt intent.

For the prosecution to be able to prove corrupt intent on the part of the defendants, however, it will need the testimony of the same businessman who allegedly offered them the corrupt quid pro quo. So it has offered him immunity for his testimony against them.

Although the immune witness strategy can be successful, it is not without risks. Defense attorneys will routinely question the veracity of any witness who testifies under a grant of immunity, and the question of that testimony effectively being “purchased” by the government can sometimes cause jurors to turn against the witness.

There is also the risk of the immune witness inadvertently becoming the “main event” at trial, with his or her own behaviors and motivations possibly overshadowing those of the defendants.

Any time the government uses immune witness testimony in a criminal case, it is an important task of the defense attorney or attorneys to thoroughly investigate the background of such witnesses, so that any weaknesses in their reasons for testifying or the testimony itself can be brought to the attention of the jury. Immune testimony can be powerful for the prosecution, but it is not always decisive in its effect.

Source: Stafford County Sun, ” U.S. granted ex-Star Scientific CEO rare blanket immunity,” Frank Green, July 14, 2014