AMARILLO, Texas (AP) - A supervisor at an Amarillo prison shoe factory died Wednesday about four hours after he was attacked by an inmate who slashed his throat, apparently with a knife.

Stanley A. Wiley, 38, first was taken to the infirmary at the Clements Unit of the Texas Department of Criminal Justice, then was transferred by ambulance to a hospital in Amarillo, prison spokesman Larry Todd said from Austin.

"We have several eyewitnesses to the assault and we plan to file murder charges as quickly as the evidence is documented," Todd said.

Wiley was pronounced dead about 11 a.m., he said.

Todd said an inmate was in custody and officials were questioning him along with others who observed the attack.

"We have several witnesses," he said. "The inspector general says there is significant evidence and eyewitnesses."

About 50 inmates were in the shoe factory when the attack occurred around 7 a.m.

Wiley, from Amarillo, joined the prison system in June 1994 as a correctional officer at the Clements Unit. In June 2000, he was promoted to the industrial specialist position, where he would oversee inmates making shoes for other offenders in the prison system.

He becomes the first Texas corrections officer to die in the line of duty since Daniel Nagle was fatally stabbed in December 1999 at the McConnell Unit in Beeville. A convicted murderer from Harris County serving a life prison term, Robert Lynn Pruett, was convicted of capital murder for Nagle's slaying and is on death row.

Todd said Travis Trevino Runnels, 26, serving a 70-year term from Dallas County for aggravated robbery, was being questioned in the attack. Runnels was not eligible for parole until 2025. He had two previous convictions and prison terms for burglary.

"We have numerous investigators on the scene talking to witnesses and gathering information," he said. "We are conducting a criminal investigation as well as an administrative review."

The prison, built in 1990 and with a capacity of over 4,000 inmates, was placed on lockdown, meaning prisoners were confined to their cells.

"We are still attempting to determine how the inmate had access to the weapon, which may have been a knife used by other inmates who trim the shoes," Todd said.

"It's very common those inmates are assigned the cutting tools while they are working but obviously they turn them back in at the end of the day's work."

For 2002 through November, the prison system reported 41 serious staff assaults, meaning they were treated for injuries that went beyond first aid from medical staff.

Gary Johnson, executive director of the prison system, promised an extensive and exhaustive investigation into events that led to the killing.

"A brutal occurrence such as this brings sorrow to every member of the TDCJ family," he said.