SALT LAKE CITY - Defendant Siale Angilau, 25, was listening to a witness describe gang-initiation rituals Monday when authorities said he grabbed a pen, rushed toward the witness, and lunged at him.

A U.S. marshal opened fire on Angilau - a "Tongan Crip" gang member known on the street as "C-Down" - shooting him several times in front of shocked jurors, lawyers, and courtroom watchers. He died hours later.

The shooting turned a new and secure federal courthouse, which had opened its doors just one week ago, into a site of terror and alarm. Nobody else was hurt, but those in the courtroom were stunned by the sudden turn of events. A mistrial was declared, with U.S. District Judge Tena Campbell saying in her order that jurors were visibly shaken and upset.

Angilau was shot in the chest - after acting in "an aggressive and threatening manner" - and died at a hospital, the FBI said in a news release. Under standard procedures, he was not restrained in the courtroom, the agency said.

Angilau was one of 17 people named in a 29-count racketeering indictment filed in 2010 accusing gang members of assault, conspiracy, robbery, and weapons offenses.

Prosecutors said he and fellow gang members robbed convenience stores and assaulted clerks in Salt Lake City on five occasions from 2002 to 2007. A clerk was shot in the final robbery, the indictment said.

Angilau's attorney, Michael Langford, declined to take questions as he left the courthouse.

The courthouse was temporarily closed after the shooting and later reopened.