BOSTON, Mass. (CBS 2/AP) — An apparent suicide brings the Craigslist killer case to a shocking end. Now Massachusetts authorities want to know how it could have happened.

Authorities withheld the precise cause of Philip Markoff’s death following Monday’s autopsy.  The Suffolk County district attorney’s office said the medical examiner’s office was still awaiting the results of specialized tests.

Guards found him dead and alone Sunday inside his Boston jail cell. His hands were bound and his head was in a plastic bag.

Markoff was accused in the killing of Julissa Brisman, a New York City-based masseuse he arranged to meet through Craigslist.

Brisman’s family and friends said Markoff’s death means they will never get a chance for justice.

“I’m being denied, as is the family, of closure, of a real closure of either having justice be served or at the same time having him say the words, having him admit that this is what he did,” said Mark Pines, Brisman’s friend.

Stephen Murphy, a Boston city councilor, has called for an independent investigation of jailhouse procedures following Markoff’s death.

“Regardless of my personal feelings about Philip Markoff, he technically was an inmate awaiting trial, and he was in the care and custody of the Suffolk County Sheriff’s Office. He had shown a penchant for doing harm to himself before. You would have thought he would have been under the closest of attention,” Murphy said.

He was also charged in the robbery of a Las Vegas woman and an attack on an exotic dancer in Rhode Island.