Blane Barksdale, 56, along with his wife, Susan Barksdale, 59, may be getting help from white supremacists, US Marshal for the district of Arizona David Gonzales said Monday.
The couple escaped custody in late August as they were being extradited to face charges of arson, burglary and murder in connection with the death of Frank Bligh, a Vietnam veteran killed in April in Tucson, Arizona. The two had used a medical emergency to get the guards to pull over to the side of the road, and then overpowered them and threw them in the back of the van, Gonzales said last month.
"Somebody like Blane in prison -- with both local -- with both state and federal prison, would be associated with Aryan Brotherhoods, white supremacist gangs. So those are the type of individuals we think that might be assisting," Gonzales said at a news conference Monday.
"I don't think there's a question that there are people that are assisting in harboring these individuals, and it is a felony," he said.
They then left the van with the guards behind.
The guards managed to free themselves after a few hours, and they notified the Apache County Sheriff's Department, Gonzales had said. By that time, the Barksdales had been gone for about six hours.
The federal agency is offering a reward of up to $25,000 for information leading to Blane Barksdale's arrest and up to $10,000 for anything that leads to Susan Barksdale's arrest, Gonzales said.
Blane Barksdale has numerous tattoos on his arms and hands.
There is also a $5,000 reward for the red GMC Sierra pickup truck the Barksdales were last seen in, he added.
"Persons placed on the US Marshals top 15 list are usually career criminals with histories of violence, and whose incident offenses pose a significant threat to public safety. Blane Barksdale has the dubious distinction of fulfilling that requirement," he said Monday.
Gonzales said authorities did not believe the two had made it into Mexico.
In April, police responded to a fire that led to an explosion at Bligh's home.
But he and his vehicle were nowhere to be found, and investigators discovered evidence the fire was set intentionally and that Bligh had been killed, Tucson police said.
On May 1, an arrest warrant was issued for the Barksdales on charges including first-degree murder, first-degree burglary, arson and auto theft, police said.
But the Barksdales had fled the state, sparking a nationwide search. They were found in Henrietta, New York, a suburb of Rochester, and arrested without incident on May 24.
Bligh's brother said the victim was good friends with Susan Barksdale but she had changed since meeting her new husband.
CNN was not able to identify an attorney for the couple.
CNN's Konstantin Toropin, Eric Levenson, Dan Simon, Giovanna Van Leeuwen contributed to this report.