Military investigators are still tying to determine what happened to a Kentucky National Guardsman nearly four months after his skeletal remains were found on a Mississippi base and urged anyone with information to contact them, authorities said Monday.

Spc. Ryan Longnecker, 19, was training at Camp Shelby in south Mississippi when he disappeared Aug. 6, 2007, just two days before his unit left for Iraq. Soon after he vanished, the military announced that Longnecker had run off with two guns and turned the case over to the U.S. Marshals Service.

His remains, however, were found by another soldier June 3 in the woods on the sprawling 136,000-acre training base between two roads and a few hundred yards from a building, authorities have said. Longnecker's two military issue weapons, an assault rifle and pistol, were found nearby.

"It is an undetermined death investigation at this point," Chris Grey, an Army spokesman, said.

The soldier's father, Bryan Longnecker, a retired Marine from Milton, Ind., said there's been much speculation about what happened, but nothing concrete has surfaced.

"It don't make no sense," Bryan Longnecker said. "I don't want to call it a possible drug overdose, but that's the only thing that's made sense to me so far."

Bryan Longnecker said Army investigators have interviewed 90 people about the mysterious death and collected cigarette butts from the scene for DNA testing. The military performed an autopsy before releasing the remains for burial in July, but have not released a possible cause of death.

"If there was somebody else there with him, maybe they'll crack," Bryan Longnecker said. "It's got to be playing on someone's conscience, if they've got one."

Col. Phil Miller, a spokesman for the Kentucky National Guard, referred questions to the Army.

Shirley Ann Longnecker of Cambridge City, Ind., the soldier's paternal grandmother, said it was ironic Ryan Longnecker was born on a military base, when his father was in the Marines, and died on a military base. She said her grandson had problems in the past, but had gotten on the right path in the Army and was eager to go to Iraq.

"The only thing I can say is that we've gone through months of racking our brains and when it comes down to it, it's still a mystery as to what exactly happened. We don't know who he might have been with or if he was by himself," she said. "I don't believe it was suicide and it's just like pieces of the puzzle are missing. Maybe as time goes on, something will unfold."

Longnecker was scheduled to deploy with the Kentucky National Guard's Battery B, 2nd Battalion, 138th Field Artillery unit when he disappeared. About 160 members of Longnecker's unit and hundreds of troops from other areas were training at Camp Shelby at the time.

"It's strange," Bryan Longnecker said. "I think if they found him sooner, maybe they would have been able to tell what happened."

Grey urged anyone with information about the death to contact police or the Army Criminal Investigation Division.