A former medical student charged with killing a masseuse he met on Craigslist has lost his request for an investigation into media leaks he claimed may have tainted the grand jury that indicted him.

An attorney for Philip Markoff last month asked a judge in Boston to order prosecutors to prove that media leaks didn't influence the grand jury.

Click here for photos from the 'Craigslist Killer' case.

Attorney John Salsberg cited news articles that included leaked evidence and possible motives for the killing of New York masseuse Julissa Brisman, 25, and the armed robbery of a Las Vegas prostitute. Markoff allegedly met both women at Boston hotels after contacting them through the erotic services section of Craigslist, which operates an online classified advertising service.

But Judge Frank Gaziano ruled that unlike jurors who sit at trials, grand jurors may "act on their own personal knowledge." He said the defense had not shown that grand jurors were influenced by bias or prejudice.

"Moreover, the defendant has not demonstrated that the indictments were improperly based on feelings of 'hatred or malice,' as opposed to indictments properly returned after the grand jury considered evidence that the defendant committed the charged crimes," Gaziano wrote in his ruling, dated Monday.

"Mere speculation that the grand jury may have been influenced by negative media reports is not enough to carry the defendant's burden of proof."

Salsberg did not immediately return a call seeking comment Thursday.

The defense alleged that law enforcement sources leaked information on evidence seized from Markoff's Quincy apartment, his use of his own name to set up an e-mail account and observations made by police of the crime scene inside Brisman's hotel room.

Markoff, 23, has pleaded not guilty in the April 10 armed robbery of a 29-year-old Las Vegas woman and Brisman's killing four days later. He also faces assault and weapons charges in Rhode Island, where he's accused of pulling a gun on a stripper April 16 at a Holiday Inn Express in Warwick.

A spokesman for Suffolk District Attorney Dan Conley said prosecutors believe the grand jury's indictments were based on the evidence they heard and not on media reports.

"In fact, it's hard to conceive of any media report that would be more powerful than the evidence developed in the past three months," said spokesman Jake Wark.