Tracy Province, 42, was caught as he walked in a sleepy town in the state of Wyoming, steps from a church where he sat in the pews a day earlier and sang "Your Grace Is Enough."
The search for inmate John McCluskey, 45, and Casslyn Welch, 44, focused for a time on sprawling Yellowstone National Park, which straddles Wyoming and Montana. But authorities now believe the two fled the park with agents following leads in Montana.
"They consider themselves as Bonnie and Clyde," U.S. Marshal David Gonzales said at a news conference in Phoenix. "This is very, very serious business."
Province, McCluskey and Daniel Renwick escaped from a private, medium-security Arizona State Prison near Kingman on July 30 after authorities say Welch threw wire cutters over the perimeter fence. Welch is McCluskey's fiancee and cousin. Renwick, who turns 37 on Tuesday, was captured in Colorado.
Efforts to find the remaining three intensified after they were linked to a double homicide in New Mexico, with the case airing Saturday on TV's "America's Most Wanted."
On Sunday, Province walked into Meeteetse Community Church, about 60 miles (100 kilometers) outside of Yellowstone, wearing blue jeans, a blue checkered flannel shirt, and a camouflage backpack slung over one shoulder, worshipper Jay Curtis said. Province looked like the many hitchhikers who pass through town.
"Just shook his hand and said 'Welcome, welcome to our church,'" said Curtis, a member of the church band. "He just smiled and said: 'Thank you.'"
Province closed his eyes and sang along with the band and seemed particularly engrossed when the band played "Your Grace is Enough" by Chris Tomlin, Curtis said.
After the service, Province walked across the street and sat down on the curb with his backpack, looking like a hitchhiker. Curtis said the church pastor then paid Province to mow and trim the church lawn. Province got $40 and a jacket, authorities said.
The town came alive Sunday night with word drifting around that the stranger at the church was a fugitive, he said. "It definitely made my wife and I and our children very nervous to think that was a convicted murderer in our town," Curtis said.
A woman who had chatted briefly with Province on the steps of the church on Sunday called police after recognizing him later on television, Gonzales said.
When marshals and other law enforcement officers arrested him, he initially denied being the fugitive, Gonzales said. He was carrying a 9 mm handgun and the sign that said "Casper," a city about 160 miles to the southeast, authorities said.
Province was in the Park County jail and scheduled for an extradition hearing Tuesday morning, authorities said.
Gonzales said a $40,000 reward was set for McCluskey and Welch's capture.
Province was serving a life sentence for murder and robbery. McCluskey was serving a 15-year prison term for attempted second-degree murder, aggravated assault and discharge of a firearm.
CBS News correspondent Ben Tracy reports that Province, McCluskey and Renwick escaped through a prison door that should have set off alarms, but didn't.
Forensic evidence linked the two inmates and Welch to the killings of a couple. New Mexico State Police spokesman Peter Olson declined to elaborate.
The badly burned skeletal remains of Linda and Gary Haas - both 61 - were found in a charred camper Wednesday morning on a remote ranch in eastern New Mexico. Their pickup truck was found later 100 miles west in Albuquerque.
Authorities believe they went to Wyoming, where Province separated from McCluskey and Welch on Wednesday morning at the southern entrance to Yellowstone.
By Monday, rangers at the park were given posters of the fugitives so they could check passing cars for them. But they weren't handing out the posters, nor were they advising entering motorists about the search. Officials said the 3,472-square-mile park was safe, as they welcomed an estimated 30,000 campers and tourists.
Wanted posters were put up at campground registration areas with pictures of the two fugitives warning: DO NOT APPROACH, attempt to contact or detain in any way.