In a recent recanvassing of the rural Pennsylvania field where Luna's body was found, investigators found a penknife that they believe caused his wounds, according to two federal law enforcement sources. They also said that investigators believe the pocketknife is the one that Luna regularly carried.
Luna was stabbed 36 times and found Dec. 4 facedown in a shallow creek in rural Lancaster County, Pa., where authorities said he drowned. His Honda Accord was nearby, its engine running.
It was not known yesterday whether authorities found fingerprints or blood on the knife, or why the weapon was not discovered during an extensive search of the scene on the day Luna was found.
The discovery of the knife comes as investigators also have sought help analyzing medical and psychological evidence from a well-regarded military forensics unit as they struggle with a new, competing theory about one of the most basic questions in the case: whether Luna was the victim of a homicide or suicide.
In FBI reports over the past month, authorities have raised the possibility that Luna, 38, could have killed himself, according to three law enforcement sources who spoke with The Sun on condition of anonymity. The controversial theory has met sharp skepticism internally, however, by a number of investigators who maintain that the evidence points to homicide.
Officials with the FBI's Baltimore field office, which has headed the investigation, have declined to comment on any of the theories that authorities are pursuing to solve the mystery of Luna's death.
"All I can say is the investigation continues," said Special Agent Barry Maddox, a spokesman for the office.
Luna's boss, Maryland U.S. Attorney Thomas M. DiBiagio, has not commented on the investigation since the night that it began, when he said preliminary evidence suggested Luna had been murdered. Vickie E. LeDuc, a spokeswoman for the prosecutor's office, also declined to comment, as has Luna's family.
The energetic and well-liked young prosecutor, who was married and had two young sons, was due in federal court in downtown Baltimore to conclude a drug case on the day that he was found dead. But investigators found no evidence that his death was related to his work, and instead have closely combed Luna's personal life for clues.
The loan application was for about $30,000, and it was canceled not long after the period when the evidence money was discovered missing, according to a federal law enforcement source. Authorities have determined that at the time of his death, Luna had credit card debts of about $25,000 -- and that he had as many as 16 credit card accounts, some that he held without his wife's knowledge.
In addition to financial troubles, Luna also had felt that he was on the outs with his supervisors in the U.S. attorney's office, where he had worked for four years. Several legal sources have said that Luna was concerned he might have to change jobs. DiBiagio has rejected any suggestion that Luna was at risk of being fired.
The highly sensitive question of whether Luna could have killed himself is at the center of a debate among investigators about the direction of the case, as it stretches into a third month with no arrests. To better develop the theory, investigators have asked the Armed Forces Institute of Pathology to examine medical and psychological evidence in the case.
A spokesman for the institute referred all questions about the Luna case to the Baltimore FBI office.
Autopsy findings by the medical examiner in Lancaster County, Pa., have not been made public, and forensic pathologist Dr. Wayne K. Ross, who performed the autopsy, has refused to discuss the case. However, the county's then-coroner, Dr. Barry Walp, said in the first days of the investigation that Luna had suffered a number of shallow "prick" marks on his chest and neck in addition to several deeper, more serious stab wounds.
While rare, there are some high-profile instances of suicides by stabbing, cases frequently marked by so-called "hesitation wounds" that barely penetrate the skin. In 1999, Army officials ruled that a National Guard captain found dead at a Kentucky base with 26 stab wounds to the neck and chest was a suicide, a finding that was disputed by the soldier's family.
More recently, the stabbing death in December of Oscar-nominated singer-songwriter Elliott Smith -- initially thought to be a suicide -- remains an open question after the Los Angeles coroner's office said it could not determine whether stab wounds to Smith's chest were most likely inflicted by him or by someone else.
If authorities conclude that Luna's death was a suicide, the finding could open investigators to allegations that they simply failed to solve the high-profile case.
Already, the case has been marked by competing jurisdictional issues between authorities in Pennsylvania and Maryland. In addition, officials in Washington are investigating whether some supervisors in the FBI's Baltimore office overreached in questioning a female agent in connection with the Luna case, a law enforcement source has told The Sun.
The internal investigation was first reported Wednesday evening by CBS News.
A federal law enforcement official said yesterday that there has been no finding in the internal probe and emphasized that investigators never considered the agent a suspect in Luna's death -- "nor have they developed any suspect," the source said.
In Luna's case, sources have described evidence that appears to run counter to a suicide theory. Officials have said that some of Luna's wounds appear to be defensive and have said that authorities found evidence of a second blood type in Luna's Honda Accord, possibly from an attacker.
Investigators also found blood on the Pennsylvania Turnpike toll ticket that they believed was turned in in rural Ephrata, Pa., when Luna's car exited the highway on the night he was killed. The ticket suggested to investigators the possibility that someone other than Luna was driving the car when it entered and left the Pennsylvania Turnpike because Luna's car had an EZ Pass card, something a driver unfamiliar with the vehicle might not have known.
In the two months since Luna's death, agents also have pored over Luna's financial records, computer files, phone logs and personal contacts in his Palm Pilot, but none of the information has led authorities to a potential suspect.