They were charged with arson, burglary, and murder when Frank Bligh, a Vietnam veteran, was killed in April in Tucson, Arizona.
The couple has faked a medical emergency or a toilet break, according to data from the US Marshal Service pulled to the side of the road.
"And when they arrived at the side of the road, they could overwhelm them, tie them up and put them in the trunk of the car they were in," said David Gonzales, US Marshal for the Arizona district.
] The guards needed time to free themselves, Deputy US Marshal Van Bayless said. When they called the police, six to eight hours had passed, he said. 
The couple allegedly had help
After the couple had tied the male and female guards in the back of the van, they drove off to a remote area in northeastern Arizona Get in touch with another person and get a new vehicle. The Barksdales then drove to a remote area, leaving the van and guards behind.
The guards were able to free themselves after a few hours and notified the sheriff department of Apache County, Gonzales said. By that time, the Barksdales had disappeared for about six hours.
"We're trying to make up for lost time," said Gonzales. Tucson police say Tuesday that the couple's driving direction is unknown, but investigators have information that they might travel through Arizona.
They were last seen driving a red GMC Sierra pickup, Arizona license plate number 1
The Sheriff Department of Pima County has suspended the use of security transport services. The company's job is to move the suspects across the country until the incident has been verified.
You are suspected of a deadly explosion.
On May 1, an arrest warrant was issued against the Barksdales, first-degree murder, first-degree burglary, arson and car theft, police said.
But the Barksdales had fled the state and launched a nationwide search. They were found in Henrietta, New York, a suburb of Rochester, and arrested on 24 May without incident.
Bligh was a veteran of the Vietnam War and was in the Air Force Reserves after the war, said the brother of the victim, William Bligh. He said his brother and Susan Barksdale are good friends, but she has changed since she met her new husband.
CNN was unable to identify a lawyer for the couple.
CNN's Konstantin Toropin and Giovanna Van Leeuwen contributed to this report.