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Posted: 11:24 AM- (Editor's note: This report was first published Aug. 24, 2003)

If Robert Matthew Mason didn't kill himself, who did? That question is one of many that keeps alive the mystery surrounding three outlaws dubbed the "Four Corners Fugitives."

Five years after the Rambo-style survivalists stole a 2 1/2-ton water truck and shot lawmen in southwest Colorado and southeast Utah, there are few answers as to what Mason and his partners, Jason Wayne McVean and Alan "Monte" Pilon, were trying to accomplish that last week of May 1998.

Without warning or provocation, they killed a Cortez, Colo., police officer and wounded two Montezuma County, Colo., deputies before fleeing into the desert of southeast Utah. It remains unclear how the water truck plays into the trio's strange plans, although some investigators speculate it could have been a precursor to an Oklahoma City-style bombing.

Clues to the band's motives may never be known unless the remaining fugitive is found alive, especially since the death of his two accomplices spawned even more questions.

Five days after the Cortez shootout, Mason's body turned up. A SWAT team found him June 4 on the south bank of the San Juan River just upstream from the southern Utah town of Bluff. Authorities announced that Mason had killed himself.

But the Utah Medical Examiner's Office would not back that conclusion. "The gunshot wound to the head had many unusual features, which would suggest that it was not a self-inflicted injury," wrote Maureen Frickke, assistant state medical examiner.

Police insist Mason slid the barrel of a 9mm Glock handgun into his mouth and then pulled the trigger. They dismiss the autopsy report -- which also details blunt-force trauma to Mason's head and bruises on his thighs and mouth -- as conjecture and see little value in probing any further the death of one of the most notorious desperados to roam the region since Butch Cassidy.

But Ann Mason views Frickke's findings as a blueprint of her son's homicide. The Durango, Colo., woman understands her son committed serious crimes but refuses to accept his death as a suicide. Taking solace from witness accounts that put Mason as the driver rather than a triggerman, she seeks closure to the episode she says destroyed her life.

"To lose a child is horrible," Ann Mason said. "But when your son goes out as one of the bad guys, it's really hard."

Pilon's death adds to the conundrum. His decomposed body was found nearly 17 months later by deer hunters not far from Hovenweep National Monument, about 50 miles from where Mason was found. An autopsy showed Pilon had suffered a broken ankle as well as a single gunshot wound to the head. But outside of one shell casing, his weapon had no ammunition, which seems unusual for a well-armed survivalist.

Law enforcement officials deemed Pilon another suicide. But, again, the Utah Medical Examiner's Office would not confirm that, based largely on the strange angle that the bullet entered the head.

Meanwhile, no one has seen or heard from McVean. That he may have gotten away keeps a pulse pumping through the mystery.

San Juan County Sheriff Mike Lacy believes McVean's bones are bleaching in the hot desert sun somewhere in southern Utah. He is loath to investigate further and is convinced that Mason and Pilon killed themselves.

"You look at criminals, like [Eric Harris and Dylan Klebold] at Columbine [High School] -- they do all this shooting, and when it comes down to the crunch, they shoot themselves."

The sheriff concedes that many particulars in the Four Corners caper don't add up. "But unless we find the other guy, we'll never know. We have 20 different theories of what happened."

Rambo rampage: In the aftermath of the rampage, investigators pieced together rough profiles of the fugitives: They fancied themselves as survivalists and would-be anti-government Rambo guerrilla fighters, preparing for the imminent dissolution of society and the chaos that would follow. They bought guns, loads of ammo and mapped southeast Utah from the Colorado border to the labyrinths of Grand Gulch west of Bluff.

Mason and McVean, both 26 in 1998, were boyhood chums from Durango. Mason had dropped out of high school and found a career in stone masonry. McVean, who authorities believe to be the leader, was a metalworker. With common interests in firearms and militias, they hooked up with Pilon, a 30-year-old mechanic from Dove Creek, Colo.

What they were up to May 28, 1998, when they stole a water truck from Ignacio, a small town southeast of Durango, won't be answered unless McVean is found alive.

Were they going to make it a bomb like Oklahoma City bomber Timothy McVeigh did with the Ryder rental? Were they going to take water to a desert hideout, where they would await the end posed by the then-pending Y2K changeover? Or would they use it as a battering ram or war wagon to rob the Ute casino at Towaoc 10 miles south of Cortez?

"That's probably as good a theory as any," Cortez police Chief Roy Lane said. "They were on a timetable. There was a timetable where an armored car would go [from the casino] to the bank every day."

Still, it remains difficult to make sense of their actions, Lane said. "None of the three was rational at the time. That's why we have so many theories. People who are rational are trying to determine what these irrational people were up to."

Their plans, whatever they were, may have changed May 29 at 9:20 a.m. as officer Dale Claxton followed the truck in Cortez. The truck pulled over of its own accord, and before Claxton could unfasten his seat belt, he was ripped by an SKS assault rifle fired by a gunman in camouflage battle fatigues and a Kevlar helmet. Claxton was hit more than a dozen times; the last shot was from point-blank range.

Horrified witnesses called 911. The chase was on.

The trio ditched the water truck and swiped an orange 1-ton Ford flatbed. As they careened through the streets of Cortez, one gunman hung out the passenger window while another fired from the truck's bed. Their firepower overwhelmed police.

Two Montezuma County deputies were wounded and a half-dozen others had their cars shot up. The flatbed raced into southeast Utah. As it sped past Hovenweep, gunmen opened up on a park ranger, who was not hit.

By early afternoon -- about 3 1/2 hours after Claxton's death -- investigators found the flatbed truck in a creek in Cross Canyon, 15 miles northwest of Hovenweep. There, they found two sets of footprints, leading some investigators to believe that Pilon had jumped or fallen from the flatbed before Mason ditched it.

Mason and McVean probably split up at that point, said Lane, who believes the pair planned to link up later on at the San Juan River. Adding to the intrigue is that Dolores County, Colo., Sheriff Jerry Martin said a boat might have been part of the escape plan.

Law enforcement agencies from around the West descended upon the Four Corners. By week's end, about 500 officers from more than 50 agencies blanketed the region. But as SWAT teams fanned out, they found nothing.

"Everybody was very apprehensive from the outset," recalled Lacy, the San Juan County sheriff. "There was confusion from the get-go on how many people we were looking at. There was confusion between the two states [Colorado and Utah] and the various agencies."

Beyond that, SWAT teams from urban areas weren't familiar with or prepared for the desert terrain. There were too many officers to control and coordinate.

"There were some management issues," Martin said. "If we had been left alone, my outfit and Lacy's outfit, and done things the way we normally do, it would have been better. We work in this area all the time."

Potential evidence -- such as fingerprints and footprints -- was lost or destroyed at several places by the hordes of police on the scene. "We lost evidence at the truck," Martin conceded.

Battle at the bridge: Despite the huge manhunt, officers turned up nothing. It wasn't until June 4 at about noon that investigators got a break when shots were fired at the car of Steve Wilcox, a Utah social worker. He had driven to a swinging bridge on the San Juan River just east of Bluff to eat lunch.

San Juan County Deputy Kelly Bradford rushed to the area. Inspecting the scene from a sandstone overlook above the bridge, he was shot twice just before 1 p.m.

"I walked toward the edge and heard a high-powered rifle shot ring out. I felt something rip through my shoulder simultaneously to hearing the shot," Bradford wrote in a report. "I dropped to my belly and began crawling toward my vehicle. . . . Within five seconds of the first shot, another shot rang out and my back exploded."

Bradford did not see the shooter. But Lane said it was the work of a marksman. "It was a tremendous shot," he said. "It was 300 yards across a canyon with an open sight."

Helicopters and law enforcement swarmed the area. Just after 5:30 p.m., a SWAT team from Pueblo County, Colo., accompanied by two trackers from the Navajo Nation Police Department spotted a rifle barrel sticking out from behind a sandy berm on the banks of the river. They spread out and launched a rapid assault approach only to find Mason already dead, investigators say.

Law enforcement officials say Mason killed himself. But the autopsy officially lists the cause of death as "undetermined."

Frickke's report also identified a foreign substance in Mason's mouth as well as bruising at its corners. That could suggest that Mason may have been gagged and killed before he was shot in the mouth.

"Paucity of hemorrhage in the tongue at the laceration suggested the possibility that the [bullet wound] may have occurred postmortem," the report states.

In addition, the autopsy detected blunt-force trauma above the eyes about the time of death, bruising between the thighs, and an injury to the right big toe.

Frickke had difficulty explaining the way blood seeped from Mason's body after his death, suggesting the body had been moved or disturbed.

But the SWAT team official whose unit found Mason said the body had not been moved. That report -- by Detective John Pannunzio -- was not issued until Nov. 19, 1998, more than five months after Mason's death.

However, Sgt. Dean Hadley, one of the Navajo trackers, said the body was turned over by members of the SWAT team. "The team leader rolled him over to ID him from a wanted poster," Hadley said.

In a Dec. 21, 1998, letter to Mason's mother, Frickke reiterated her concerns -- including that the bullet had inexplicably expanded in the tongue.

"Because of this unusual finding," she wrote, "I suggested to the representatives of the Colorado Bureau of Investigation, who attended the autopsy, that they determine whether the projectile recovered from Robert [Mason] had, in fact, been fired from the firearm that was lying beside him. I have not been informed of any test results relating to these questions."

Although some law enforcement officials vehemently disagree with Frickke's findings, a review by Michael Dobersen of the Arapahoe County Coroner's Office in Colorado "generally agreed with the determination made by Dr. Frickke."

In a Feb. 12, 2001, letter to Ann Mason, Dobersen said, "some features of the gunshot wound are suspicious," including the bullet fragments in the tongue.

"Also of concern were other injuries to the head which do not appear to be associated with the gunshot wound," Dobersen wrote.

But the San Juan County sheriff doubts ballistics tests will shed any more light on the shooting. Glocks, which police often carry, are made with plastic barrels and do not produce "riflings," the distinct impression left on slugs by firearms with steel barrels.

"A lot of times with Glocks, you can't tell which gun a [slug] came from," Lacy said.

In an undated "abstract" titled "Robert Mason Death Investigation," former San Juan County Deputy William Pierce dampened the autopsy's findings. He suggested the unusual expansion of the hollow-point bullet could have been caused by "plant material, dirt and other fibers" in the barrel.

Pierce also speculated Mason may have fractured his own skull inadvertently. "In reconstructing the events of June 4, 1998, it was determined the blunt force injuries could have been self-inflicted, though not necessarily intentionally."

Mason's thighs could have been bruised when he crossed the swinging bridge, Pierce surmised. "It is natural to assume, as was verified during my re-enactment, that an individual crossing the bridge in haste, carrying various items, would stumble and fall."

So whodunit? In the end, there are three possible explanations for Mason's death: He shot himself. McVean shot him. Or police shot him.

Lacy quickly rules out the last two possibilities.

If a law enforcement officer had killed Mason, he would have been a hero, Lacy explained. "Most officers would brag about it, 'I got the son of a gun.' "

The sheriff also dismisses the motion that McVean shot his partner and then escaped down river.

"There are no other footprints," he said. "We tracked [Mason] all the way [up the San Juan River] back to Montezuma Creek."

But what if McVean approached from another direction, and his footprints became obscured when SWAT teams swooped in? There were so many footprints in the area that the casing from the 9mm Glock was thought, in at least one report, to have been stomped inadvertently into the sand.

That casing never was found.

And there remains the possibility of a boat. Witnesses say they saw Pilon in Bluff two weeks earlier with some kind of watercraft in the back of a pickup.

"I'm convinced they had a boat," said Martin, the Dolores County sheriff. "They had a plan of escape and there may have been a fourth guy."

That Mason was found near the swinging bridge is more than a coincidence, noted Lane, the Cortez police chief. "It was a rendezvous point," Lane said.

Add to that witness accounts of two men in a boat floating under the highway bridge shortly after Bradford was shot near the swinging bridge and the mystery becomes the stuff of lore.

But none of the leading investigators in Utah or Colorado wants to believe that McVean got away. Whether Pilon was shot by one of his partners is something Martin and Lane will at least consider. The fact that he was found without ammo with an unlikely suicide wound could point to murder.

The difference between the two dead desperados is that unlike Pilon, Mason and McVean were longtime friends.

That leaves Ann Mason with the gnawing suspicion that her son may have been beaten to death by lawmen who then faked his suicide.

"I can't say my son is innocent. My son was up to something. But I think he realized it had gone wrong very fast," she said.

Because Mason was one-quarter American Indian and died on a reservation, she wants the FBI to investigate. But the bureau refuses.

"The walls and lack of truth I'm getting are as hard as his death. I haven't gotten any closure," Ann Mason said. "Our story will never have a happy ending, but we need an ending of some kind."