The search for a death row inmate who walked unnoticed out of a Texas county jail become a nationwide manhunt Saturday as authorities investigated whether he had help making the brazen escape.

The U.S. Marshals Office (search) offered a $10,000 reward for the capture of Charles Victor Thompson (search) and designated him a federal fugitive. Officials also alerted airports, border officials and other law enforcement agencies.

"This is an extensive search," said Lt. John Martin of the Harris County Sheriff's Department. "We are relying on the public to report any information that they have."

Thompson, 35, of the Houston suburb of Tomball (search), escaped Thursday after meeting with an attorney, though not his defense attorney of record, authorities said. He was condemned in 1999 for the shooting deaths of ex-girlfriend Dennise Hayslip, 39, and her boyfriend, Darren Keith Cain, 30.

Martin said Saturday that investigators had found the civilian clothing Thompson wore when he left the building. It was behind one of the sheriff's department's other downtown jail buildings, and some effort had been made to hide it, he said.

"It's pretty clear at this point there was somebody helping him," Martin said.

Authorities also found the fake ID badge Thompson used, which turned out to be an inmate ID card with his photograph issued by the Texas Department of Criminal Justice (search). Thompson had put a piece of tape over the part of the card that indicates he is an inmate.

Thompson was in the county jail awaiting transfer to a state prison. A jury sentenced him to death Oct. 28 after an appeals court threw out an earlier sentence.

On Thursday, Thompson was taken to a room in the jail for a meeting with his attorney. The visitor, however, was not Thompson's attorney of record, Terrence Gaiser.

Martin said investigators have determined the other person was an attorney, but his name was not released because he is considered a witness.

"We are not necessarily suggesting he was involved with the escape, but we will be speaking with everybody who had contact with Thompson," Martin said.

After the visitor left, Thompson removed his handcuffs and his bright orange prison jumpsuit and got out of a prisoner's booth that should have been locked. He then left wearing a dark blue shirt, khaki pants and white tennis shoes, and claiming to work for the Texas attorney general's office.

Authorities believe the clothes were the same that Thompson wore during his sentencing. Martin said Thompson somehow smuggled them back to his cell.

Prosecutors had accused Thompson of trying to hire hitmen to kill witnesses against him as well as members of Hayslip's family, and Martin said that members of Hayslip's family had been given police protection.

"There is no good way to spin this," he said. "The point is there were multiple errors on the part of our personnel. This is 100 percent human error that could have been prevented and it wasn't."

Cathy Lange, who served on a resentencing jury that recommended the death penalty for Thompson on Oct. 28, said she was terrified when she learned of Thompson's escape.

"He can make people believe he is the most innocent man in the world," Hayslip's mother, Wynona Donaghy, told the Houston Chronicle. "If somebody is helping him, they don't realize how dangerous he is."