U.S. authorities planned an autopsy on Monday of a man found dead in his Boston prison cell more than a year after being charged with murdering a masseuse he met on Craigslist, a law enforcement official said.

Philip Markoff, 24, was found on Sunday in the Nashua Street Jail with a plastic bag over his head and cuts on his arms in what local media described as an apparent suicide.

The former medical student had been awaiting trial in Massachusetts for the armed robbery and murder of Julissa Brisman, who was shot in a Boston hotel in April 2009, and the armed robbery of another woman in Boston around the same time.

Prosecutors alleged that Markoff committed the crimes after meeting the women through the Craigslist.org Internet advertising service, which is partly owned by online auctioneer eBay Inc.

Dubbed The Craigslist Killer by some media, Markoff pleaded not guilty to the charges. He was also accused of attacking a woman in Rhode Island in a separate case.

We expect to have a preliminary cause of death by later today, said Jake Wark, a spokesman for the Suffolk County District Attorney.

Brisman's murder prompted Craigslist to drop its erotic services ad category, replacing it with an adult category that the company said would be closely screened.

In May, Connecticut authorities said they were investigating whether the company was doing enough to prevent its users from advertising prostitution, which is illegal in most of the United States.

(Reporting by Scott Malone and Svea Herbst-Bayliss; Editing by Paul Simao)