URGENT: Authorities say there's a "significant development" in the search for two convicted killers who escaped from an Arizona prison and cut a deadly path north to Yellowstone National Park, where over 100 federal agents are hunting for them.

The U.S. Marshals Office and Arizona authorities said Monday they will make an announcement about the case, even as armed park rangers and federal agents searched in and around tourist-packed Yellowstone, where an estimated 30,000 people entering the park were warned about the search.

U.S. Marshals believe Tracy Province, John McCluskey and Casslyn Welch may be hiding in portions of Yellowstone that span Montana and Wyoming. Efforts to find the trio have intensified after one of the inmates was linked to a double homicide in New Mexico.

Authorities tell Fox News that it's now believed that Province has separated from McCluskey and Welch, who are first cousins and common-law husband and wife.

It doesn't appear any of the three are expert campers or have wilderness survival skills, and the Marshals service believes they could be staying in campgrounds and at truck stops.

"They are very dangerous individuals, very desperate individuals, and the longer they're out there, the more desperate they become," said Thomas Henman, supervisory deputy with the U.S. Marshals Service in Phoenix.

"From the start, we believed these individuals would be staying at campgrounds and truck stops and other places like that. This keeps to that pattern," Henman said. He added authorities believe the three might be sticking to back roads and smaller state highways.

Visitors were being apprised of the situation, but some campers tucked deep in the rugged wilderness are likely to be unaware of the manhunt.

"They just don't have any regular access to any news because of the remote nature of the place," park spokesman Al Nash said. "The bottom line is, it's safe, everything's open and park visitors should not be unduly concerned."

U.S. authorities have advised the Royal Canadian Mounted Police that the suspects may try to cross into Canada, Henman said. The warning was issued because the three have quickly moved northward and were within several hundred miles of the border, he said.

Province, McCluskey and Daniel Renwick escaped from the medium-security Arizona State Prison near Kingman on July 30 after authorities say 44-year-old Welch of Mesa threw wire cutters over the perimeter fence. Renwick was arrested in Colorado on Aug. 1.

The badly burned skeletal remains of Linda and Gary Haas, both 61, of Tecumseh, Okla., were found in a charred camper on Wednesday morning on a remote ranch in Santa Rosa in eastern New Mexico.

Olson said a car belonging to the couple was found 100 miles east in Albuquerque on Wednesday afternoon.

The Arizona Department of Corrections says the three men escaped by cutting a hole in the prison's perimeter fence and later kidnapping two semi-truck drivers at gunpoint and using the big rig to flee. The group left the drivers unharmed in the truck at a stop just off Interstate 40 in Flagstaff and then fled.

Province was serving a life sentence for murder and robbery out of Pima County. McCluskey was serving a 15-year prison term for attempted second-degree murder, aggravated assault and discharge of a firearm out of Maricopa County. Renwick had been serving a 22-year sentence for second-degree murder.

A nationwide search was under way for McCluskey, Province and Welch. The group may be using a 1997 platinum gold Nissan Sentra with Arizona license plate 620PFV.

The Associated Press contributed to this report