BOSTON -- Accused “Craigslist Killer” Philip Markoff committed suicide at Nashua Street Jail in Boston, where he was being held awaiting trial in the slaying of a woman who was visiting from New York, according to a spokesman for the Suffolk County Sheriff's Office.

Officials do not know how he died, officials said. Markoff, 24, was pronounced dead at 10:17 this morning.

Authorities have said that Markoff shot Julissa Brisman, who was visiting Boston from New York, three times with a handgun on April 14, 2009 after they struggled in the doorway of her room on the 20th floor of the Marriott Copley in Boston. A bullet pierced her heart. Prosecutors said Markoff also battered her head.

He had been placed on suicide watch shortly after his arrest nearly a week after the slaying.

Markoff, a former Boston University medical student, pleaded not guilty to homicide and armed robbery charges.

Markoff was also charged with armed robbery and kidnapping in two similar incidents in which the victims were not injured. Prosecutors contend that Markoff preyed on prostitutes and erotic masseuses he met at hotels after seeing the women's ads on the Craigslist website.