Baltimore ? Federal prosecutor Jonathan Luna was stabbed 36 times in a furious fight for his life before drowning in a Pennsylvania creek, investigators said Friday as they worked to reconstruct his final hours.

A federal law enforcement official, speaking on condition of anonymity, said authorities had not established a motive for the slaying — the first killing of a federal prosecutor in two years.

Investigators are interviewing people connected with cases Luna prosecuted, as well as friends and associates, but no immediate promising leads have come up, the official said.

Luna apparently was attacked after leaving his office in Baltimore around midnight Wednesday, the source said. His body was discovered six hours later and 70 miles away, near his blood-smeared, idling car, according to a police affidavit.

Lancaster County, Pa., coroner Dr. Barry Walp said the 38-year-old assistant U.S. attorney was “brutalized with multiple stab wounds” that could have been caused by a penknife, and then drowned in the creek.

“They were defensive wounds,” a second federal law enforcement source told The Associated Press on condition of anonymity.

Walp said Luna was dressed in a suit and overcoat, and had his wallet with identification and cash, but it was unclear whether he had been robbed.

Money and cell phone equipment also were found inside his car, which had blood on the driver’s side door and fender and a large pool of blood on the floor, according to a police search warrant application. The affidavit said Luna also had a “traumatic wound” on the right side of his head.

The FBI worked to create a timeline of what Luna did in his last hours.

By 5 p.m. Wednesday, Luna and defense attorneys had reached a plea bargain in the case of rap musician Deon L. Smith and Walter O. Poindexter, who were on trial on charges of running a violent heroin ring from their studio, according to the judge presiding over the case.

Poindexter’s attorney, Arcangelo Tuminelli, said he got a call from Luna at 9:06 p.m. in which the prosecutor said he was still drawing up the paperwork for the plea and making sure it was all correct.

Tuminelli said he did not know where Luna was then. But he said Luna told him he had to go home and would be back in his office in the federal courthouse in Baltimore later.

“I assumed there would be a fax at my house of the agreement by about midnight,” Tuminelli said. The fax never came.