Assistant U.S. Attorney Jonathan P. Luna (search) was "brutalized with multiple stab wounds" and left to drown in the Pennsylvania creek where his body was found, a coroner said Friday.

The 38-year-old man was still alive when he was left in the creek, said Lancaster County, Pa., coroner Dr. Barry Walp. He was stabbed 36 times in a furious fight for his life before drowning, investigators said Friday as they worked to reconstruct his final hours.

A federal law enforcement official, speaking on condition of anonymity, said authorities have 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.

Walp said the stab wounds could have been caused by a penknife.

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

Luna's body was discovered face down in the water, law enforcement officials told Fox News. The damage done to the body was "nothing less than gruesome," one official said.

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 (search) and Walter O. Poindexter (search), 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 where Luna was at that point. 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.

One federal law enforcement official said authorities had determined Luna left his home early in the evening and went back to his office to work on papers in the plea bargain. He was there until around midnight, the source said.

Another source who spoke on condition of anonymity said there were personal items in Luna's office that one "would have expected him to be taking home had he been leaving to go home for the evening." The source declined to describe the items.

Authorities have not said whether the rapper's case had anything to do with the slaying. Smith and Poindexter were behind bars at the time.

Tuminelli said the FBI interviewed Poindexter on Thursday night.

"He had absolutely no information that would be of help to them," he said. "I believe that this has nothing to do with my client or Mr. Smith."

Tuminelli said Smith also consented to be interviewed by authorities.

"What happens in the rap world aside, I'm telling you with my knowledge of this case, I'm telling you it's an implausible suggestion," that the two rappers could have been involved in Luna's murder, Tuminelli later told Fox News.

"It's unfair to Mr. Poindexter and to Mr. Smith as well as to Mr. Luna to suggest that these men are responsible or may be responsible," for the murder, he said.

The last federal prosecutor to be slain was Assistant U.S. Attorney Thomas C. Wales, who was shot to death in Seattle in October 2001. That slaying remains unsolved.

Friends and relatives visited Luna's family at their home in Elkridge.

Luna was "always out, always saying hello, always playing ball with the kids, always outside with the kids in back," neighbor Dana Stango said. "Very, very tight family knit ... The perfect family. It's not fair."

Fox News' David Lee Miller, Anna Stolley and The Associated Press contributed to this report .