Federal prosecutors say a New Jersey man must testify if he intends to claim he tried to warn authorities a co-defendant wanted to kidnap and kill women.

Prosecutors in New York asked a judge Tuesday to block defense claims about statements Michael Vanhise (van-HYS') made to FBI agents. They say if the defense wants the jury to hear that information, it should come directly from the defendant.

If he testifies, he'd be cross-examined by prosecutors.

Jury selection starts Feb. 24 for Vanhise and a former Manhattan high school librarian.

Vanhise is charged in a conspiracy to kidnap, rape and kill women. He's accused of discussing violent topics online. He says he just wanted to gather information so police could make arrests.

The Trenton resident has been held without bail since his January 2013 arrest.