A grand jury will investigate the death of Julia Papazian Law, the 26-year-old paralegal found dead in a bathtub in her boss' Center City apartment last month.

Word of the inquiry came as toxicology tests revealed that at the time of her death, Law had a blood-alcohol level higher than 0.40 percent - five times the threshold for legal intoxication, according to court sources. Medical experts say a blood-alcohol content of 0.35 percent or greater may be fatal.

The District Attorney's Office confirmed Friday that it had asked for the grand jury probe, but declined to elaborate.

Law, who worked for high-profile defense lawyer A. Charles Peruto Jr., was found facedown in his tub on May 25.

Peruto, 58, who described Law as his girlfriend, told police he was in Avalon, N.J., on the night she died. He said he learned of her death from a maintenance worker who found her body in Peruto's Rittenhouse Square apartment.

Asked about the grand jury, Peruto said, "I've been told they are not investigating me, they are investigating the death, and there's a big difference." He declined to comment further, saying police had asked him not to discuss the matter.

From a prosecutor's standpoint, a grand jury investigation offers mandatory secrecy that can ease the fears of reluctant witnesses. It also allows prosecutors to compel testimony from witnesses by offering them immunity from prosecution.

In the past, Philadelphia prosecutors have turned to the grand jury in complex investigations, such as the 2010 jury that recommended criminal charges against West Philadelphia abortion doctor Kermit Gosnell.

Last June, the state Supreme Court expanded the role of grand juries, giving them power to bring criminal charges.

It is not known why prosecutors decided to use the grand jury in the Law case.

Officials have said there were no signs of a struggle and no physical trauma to Law's body. Although the city Medical Examiner's Office has not released an official cause of death, law enforcement officials familiar with the investigation have said she likely drowned.

Peruto told police that Law had sent him text messages late into the night before her body was found the following morning.

Her family has said the woman, who grew up in Absecon, N.J., had been going through a difficult time after a romantic breakup with another man.

Contact Joseph A. Slobodzian at 215-854-2985, jslobodzian@phillynews.com, or @joeslobo on Twitter.