(CNN) -- An autopsy was conducted Monday in the death of a onetime medical student who died of an apparent suicide while facing charges in a killing tied to the Craigslist website.
However, the medical examiner is withholding the official cause of death for Philip Markoff pending further tests, prosecutors said.
"Markoff was alone in his cell and all evidence collected thus far indicates that he took his own life," Boston Police Commissioner Edward Davis and Suffolk County District Attorney Daniel F. Conley said in a statement released earlier. "Nonetheless, as with all such cases, a comprehensive investigation will be conducted to determine the facts and circumstances surrounding his death."
Suffolk County Sheriff Andrea Cabral told CNN that Markoff had not demonstrated any notable behavior while in custody and did not pose a disciplinary problem before his death. While Markoff had been on suicide watch from April 23 to May 14, he was not on watch around the time he died, she said.
Suicide watch for jail inmates is determined by a psychiatrist, she said. In her eight years as sheriff, there have been four confirmed suicides; Markoff would be the fifth. There's an average of 57 serious suicide attempts a year, Cabral added.
Markoff was found unresponsive in his Boston, Massachusetts, jail cell at 10:17 a.m. Sunday and pronounced dead by medics, according to officials. He was found with wounds to his neck and ankles, EMS spokeswoman Jennifer Mehigan said.
Markoff, 24, was charged with the April 14, 2009, fatal shooting and attempted robbery of Julissa Brisman, 25, at Boston's Copley Marriott Hotel.
Police said that Brisman, a model, advertised as a masseuse on Craigslist, a popular online classifieds service, and said Markoff might have met her through the site.
In a statement Sunday, the family of Brisman said it was "shocked and dismayed" at the news of Markoff's apparent suicide.
"Their grief for Julissa is as fresh today as the day over a year ago when Markoff took Julissa away from them," said the statement issued by a representative for the family. "The long-awaited criminal prosecution was their only opportunity to confront him, and now he has taken that away as well."
The family promised to pursue "other avenues to seek justice for Julissa and help ensure that others do not suffer from such devastating, unnecessary violence," according to the statement.
Markoff was also charged with the April 10, 2009, robbery of Trisha Leffler at a Westin Hotel in Boston. Police reports said Leffler was robbed of $800 in cash and $250 in American Express gift cards and was held at gunpoint and bound.
At his arraignment in June 2009, Markoff pleaded not guilty to the Massachusetts charges.
He also was facing charges in an April 16, 2009, incident at a Holiday Inn Express in Warwick, Rhode Island.
In that incident, police said, Markoff tied up and demanded money from a 26-year-old dancer who had posted a Craigslist advertisement. The robbery was interrupted when the woman's husband entered the room, and the suspect fled after pointing his gun at the husband, according to Warwick Police Chief Col. Stephen McCartney.
At the time of his April 2009 arrest, Markoff was a second-year student at Boston University's School of Medicine and was engaged to be married. His friends and acquaintances expressed shock, describing him as a model student and the "all-American" guy.
A woman identifying herself as Megan McAllister, his fiancee, maintained his innocence in an April 2009 e-mail sent to ABC News, saying Markoff "is the wrong man" and "was set up."
"Unfortunately, you were given the wrong information as was the public," she said. "All I have to say to you is Philip is a beautiful person inside and out and could not hurt a fly!"
Markoff's attorney had also proclaimed his innocence.
Conley, the district attorney, told reporters last year that Brisman's death was "a brutal, vicious crime -- savage. And it shows that Philip Markoff is a man who's willing to take advantage of women -- to hurt them, to beat them, to rob them."
Brisman sustained blunt head trauma and was shot three times at close range, prosecutors said. Conley said they believed the motive for her death was robbery.
In executing a search warrant at Markoff's home, police found a firearm, along with restraints and duct tape, he said.
Police traced internet communications with Brisman to an e-mail account that had been opened the day before her death, Conley said. Using internet provider information, they found the computer was at Markoff's residence in the Boston suburb of Quincy, he said.
CNN's John Branch and Logan Burruss and In Session's Beth Karas contributed to this report.