Editor's note: The Associated Press has combed through the results of 2 1/4 years of investigations and uncovered some startling findings about the death of Pat Tillman, a football player who walked away from an NFL contract to serve in the U.S. Army Rangers. This is the last of three parts.

By SCOTT LINDLAW

and MARTHA MENDOZA

The Associated Press

The veteran Pentagon official who is overseeing the latest inquiries into the death of Pat Tillman, acting Defense Department inspector general Thomas Gimble, has called the probe the toughest case he has ever seen, according to people he recently briefed.

Investigators are looking at who pulled the triggers and fired at Tillman; they are also looking at the officers who pressured the platoon to move through a region with a history of ambushes; the soldiers who burned Tillman's uniform and body armor afterward; and at everyone in the chain of command who deliberately kept the circumstances of Tillman's death from the family for more than a month.

Military investigators under Gimble's direction this year visited the rugged valley in eastern Afghanistan where Tillman was killed. It was a risky trip; the region is even more dangerous today than it was in 2004.

According to one person briefed by investigators, the contingent included at least two soldiers who were there the day of the incident -- Staff Sgt. Matthew Weeks, a squad leader who was up the hill from Tillman when he was shot, and the driver of the vehicle that carried the Rangers who shot Tillman, Staff Sgt. Kellett Sayre.

When the current inquiry began, the Pentagon projected it would be completed by September 2006. Now Gimble and the Army's Criminal Investigation Command, known as CID, are aiming to finish their work by December, say lawmakers and other officials briefed by Gimble.

CID is probing everything up to and including Tillman's shooting. The inspector general's office itself has a half-dozen investigators researching everything that happened afterward, including allegations of a coverup.

The investigators have taken sworn testimony from about 70 people, some of whom said they were questioned for more than six hours. But Gimble said investigators have been hindered by a failure to locate key witnesses, even some who are still in the active military.

Moreover, those who are now out of the Army, including three of the four shooters, can't be court-martialed. They could be charged in the civilian justice system by a federal prosecutor, but such a step would be highly unusual.

The law that allows it, the Military Extraterritorial Jurisdiction Act, has been invoked fewer than a half-dozen times since its enactment in 2000, said Scott Silliman, executive director of Duke Law School's Center on Law, Ethics and National Security and a high-ranking Air Force lawyer until his retirement in 1993.

The investigation, Gimble has said, is also complicated because of "numerous missteps" by the three previous investigators, particularly their failure to follow standards for handling evidence.

Gimble promised lawmakers in a series of briefings this fall that his investigation "will bring all to light." He has committed to releasing his detailed findings to key legislators, Pentagon officials and the Tillman family, as well as a synopsis to the general public, congressional aides said.

Gimble declined an AP request for an interview.

Seven disciplined

To date, a total of seven soldiers have been disciplined in Pat Tillman's death.

Lt. Col. Jeffrey Bailey, the 2nd Ranger Battalion commander who was camped out about two miles down the road with another unit the night Tillman died, surveyed the shooting scene hours after it occurred.

"I don't think there was any criminal act," he said. "It was a fratricide based upon a lot of contributing factors, confusion," he testified to an investigator in late 2004.

Some high-ranking officers, including Bailey, believe a lack of control in the field was to blame -- starting with the platoon leader and including the soldiers who didn't identify their targets.

Bailey, who approved punishments for several of the soldiers, said he disagreed with the platoon's protests that they were "doing what we asked them to do under some very difficult circumstances, and that there were mistakes made but they weren't negligent mistakes."

He also testified that "three gunners were, to varying degrees, culpable in what had happened out there." And he said he wanted a fourth soldier involved -- the squad leader, Baker -- "out of the military."

Baker soon left the Army.

As for others involved:

* The three other shooters -- Spc. Stephen Ashpole, Staff Sgt. Trevor Alders and Spc. Steve Elliott -- remained in the service initially but Elliott and Ashpole have since left. Elliott struck a deal with authorities; in exchange for his testimony to investigator Brig. Gen. Gary M. Jones, the Army gave him immunity from prosecution "in any criminal proceedings."

* The platoon leader, Lt. David Uthlaut, was later bumped down from the Rangers to the regular Army for failing to prepare his men prior to the shootings, according to Bailey.

"They didn't do communications checks. They didn't check out their equipment. So they'd been there 24 hours," Bailey testified. "For example, some of the weapons systems weren't even loaded with ammunition. Many of the soldiers didn't know where they were going. They didn't have contingency plans."

A non-commissioned officer on the ground that day, however, testified that the unit carried out required communications checks.

Uthlaut was also wounded by fellow Rangers in the incident. He was awarded the Purple Heart and later promoted to captain.

* Capt. William C. "Satch" Saunders, the company commander, was given the authority to punish three soldiers. Both Saunders and Maj. David Hodne received formal written reprimands for failing to "provide adequate command and control" of subordinate units -- administrative punishments lighter than the Article 15s handed down to the soldiers who shot at Tillman. This obviously hasn't hurt Hodne's career; he has since been promoted.

"I thought it was [the commanders'] fault, or part of their fault that we were even in this situation, when they're telling us to split up," said Ashpole.

Some lawmakers have warned that if this probe does not clear up all questions on Tillman's death, they may press for congressional hearings. Others have said Congress could call for an independent panel of retired military officers and other experts to conduct an outside probe.

Rep. Mike Honda, a Democrat who represents the San Jose district where Tillman's family lives, has pressed the Pentagon for answers on the status of its investigations.

"I'm very impatient and at times cynical," Honda said. But, he said, the honor of the military -- and the confidence of the public in the military and the government -- are at stake.

"So if we pursue the truth and wait for it," he said, "it may be worthwhile."