Notorious Boston gangster James “Whitey” Bulger was found dead Tuesday morning at a West Virginia prison.

It was not immediately clear if the 89-year-old was killed, as some news reports said, or died from other causes.

Bulger was found unresponsive and “life-saving measures were initiated immediately by responding staff,” the Federal Bureau of Prisons said in a news release. “Mr. Bulger was subsequently pronounced dead by the Preston County Medical Examiner.”

The FBI has launched an investigation into the death, the news release said.

Bulger was being held at maximum penitentiary USP Hazelton in West Virginia, where he had been relocated on Monday.

Bulger, the former leader of the Winter Hill Gang, was convicted in 2013 of participating in 11 murders across the U.S. and was serving a life sentence.

He spent 16 years on the run before he was captured in Santa Monica, Calif., in 2011.

He was recently relocated from a Florida prison to a facility in Oklahoma before being transferred to the West Virginia prison.