Updated

The trail has gone cold in the search for an escaped Arizona inmate and his suspected accomplice, with baffled federal authorities saying they have no idea where the couple is and warning travelers stopping at campgrounds and truck stops to be alert.

John McCluskey and Casslyn Welch, two of the most wanted fugitives in America, are unpredictable and have long-haul truck driving experience, meaning they are used to driving long distances over short time periods, Fidencio Rivera, chief deputy U.S. Marshal for Arizona, said Thursday. Their route has crossed more than 1,900 miles from their July 30 escape from a medium security prison in Arizona to the last concrete sighting in Billings, Mont., last Friday

"At this point in time, because they move so quickly and easily, we have no idea," Rivera said. "In two-and-a-half days they could have traversed the entire United States. They can be anywhere."

Marshals are asking travelers at truck stops along highways and in campgrounds across the nation to watch out for the couple, who may have dyed their hair and otherwise changed their appearance. They may be sleeping in campgrounds and using truck stops to clean up as they travel in a 1997 Nissan Sentra that has been described separately as gray, gold and tan, Rivera said.

Authorities believe McCluskey, 45, and Welch, his 44-year-old cousin and fiancee, are dangerous and have been paying for their getaway by robbing businesses along the way. They and fellow escaped convict Tracy Province, who split from the group and was arrested in Wyoming on Sunday, also are suspects in the deaths of an Oklahoma couple whose burned bodies were discovered last week in eastern New Mexico.

"We're concerned that these individuals will commit more crimes," Rivera said. "They're desperate. These guys are not thinking rationally."

Little is known about the background of the couple whom authorities say fashion themselves a modern Bonnie and Clyde. McCluskey was serving 15 years in prison for attempted murder, aggravated assault and discharge of a firearm. He also served 14 years in Pennsylvania state prisons for a string of convenience store robberies in April 1992.

Welch is from Arkansas, where she still has family.

McCluskey, Province and Daniel Renwick broke out of the northwest Arizona prison when Welch threw wire-cutting tools over a fence and the criminals sliced their way through the fence, authorities said.

But the four became disoriented and could not find their getaway car — which Welch had parked nearby with cash, weapons and false identifications, Rivera said.

The group split up, and Renwick found the vehicle and drove off, leaving the other three to hijack a vehicle and head toward Flagstaff in a journey that has included sightings in Amarillo, Texas, Santa Rosa, N.M, and Yellowstone National Park, Wyo.

Renwick was arrested two days after the jailbreak in Rifle, Colo., where he allegedly shot at a pursuing officer in hopes that police would kill him, according to court documents.

Police searched the Chevy Blazer driven by Renwick and found a HiPoint .40 caliber model 4095 rifle and 141 rounds of ammunition, as well as nine spent .40 caliber cartridges. Police also found pillows, a blanket, $2,925 cash, marijuana, drug paraphernalia and a black purse, as well as a driver's license belonging to a California man. Officers also found blood in the vehicle, but they don't know whose.

New Mexico authorities have said forensic evidence links the group to the deaths of an Oklahoma couple whose bodies were found in their charred camper in the eastern part of the state a week ago. The badly burned skeletal remains of Linda and Gary Haas — both 61 and from Tecumseh, Okla. — were discovered on a remote ranch in eastern New Mexico.

"We believe at that point of time they were together, though who did what, we have no idea, whatsoever," Rivera said. "We defer to the New Mexico state police."

New Mexico state police have declined to elaborate on the deaths.

The search for the couple abruptly turned from Montana to Arkansas on Wednesday when a pair matching their description robbed a beauty salon in the town of Gentry. Officials in Arkansas say they have "no reason to believe" that McCluskey and Welch had pulled off the heist, but U.S. marshals say the leads there have not been exhausted and the investigation is continuing.

Benton County Sheriff's Office spokesman Doug Gay said Thursday that the extensive search around Gentry was expected to be scaled back.

"We'd like to know if these are the pair from Arizona," Gay said. "All indicators point to no."

Salon owner Joyce Cook was alone at her business Wednesday morning when a couple entered and the woman said she wanted a haircut. Then the man pulled a gun, tied her up with rope and stole money.

Gay said Cook was shown photographs of the fugitives, and even though officials believe they have changed their appearance — Welch dyeing her hair blond and McCluskey dyeing his black — Cook was certain they were not the couple in her shop.

"She didn't have blond hair and it had not been recolored. I would have recognized that immediately," Cook said. The woman had brown hair with a reddish cast, Cook said.

Another difference: Cook said the male robber did not have visible tattoos, as McCluskey does.

Meanwhile, the search is still on in Montana. Two days after the couple was seen in Billings, Welch was reportedly spotted in the town of St. Mary just east of Glacier National Park. The report prompted authorities to converge on the wild, open land of the Blackfeet Indian Reservation and to check cars crossing the border into Canada.

Marshals have not been able to corroborate that sighting, Rivera said Thursday, though patrols in the region and at the border are continuing.

"There's been absolutely nothing (new) in this area since the Sunday sighting at St. Mary," said Wade Muelhoff, spokesman for Glacier National Park, where officials are assisting U.S. marshals in the search.

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Juozapavicius reported from Gentry, Ark. AP writers Peter Banda in Glenwood Springs, Colo., and Mark Carlson in Phoenix contributed to this report.