WATCH: Investigators to Comb Deadly Prison Bus Crash Site in Texas

ODESSA, Texas (AP) — Investigators trying to determine the cause of a West Texas prison bus crash that killed eight inmates and two guards were returning to the site Thursday to sift through the debris and examine the vehicle.

The state Department of Criminal Justice bus skidded on an icy overpass, slid down an embankment and collided with a passing Union Pacific freight train Wednesday morning, leaving the bus a crumpled mass and scattering packages from the train alongside the track in Penwell, just west of Odessa.

Eight prisoners and two long-time veteran prison department officers, including the driver, were killed, the agency said in a statement. Another corrections officer and four other inmates were hospitalized.

"It's as bad as you can imagine," Odessa Fire and Rescue Battalion Chief Kavin Tinney told the Odessa American newspaper Wednesday. "In 32 years, it's as bad as anything I've seen."

The prisoners did not have seat belts and were handcuffed together in pairs, officials said. Some of them were ejected from the bus after it struck the train, said Trooper Elizabeth Barney of the Texas Department of Public Safety. Jason Heaton, agency director for the region, said the prisoners were not wearing leg restraints, and that the driver's seat had a seat belt.

An earlier accident on the I-20 overpass may have contributed to the prison bus losing control, Ector County Sheriff Mark Donaldson said, adding that the road had been slick with ice.

A state prison system spokesman said the bus was new and had been placed in service over the summer.

National Transportation Safety Board and Texas Department of Public Safety officials planned to investigate further on Thursday.

A prison system statement identified the correctional officers killed as Christopher Davis, 53, and Eligio Garcia, 45. The inmates killed were Byron Wilson, 34; Tyler Townsend, 29; Jesus Reyna, 44; Kaleb Wise, 22; Adolfo Ruiz, 32; Michael Sewart, 25; Angel Vasquez, 31; and Jeremiah Rodriguez, 35.

Davis had more than 17 years of service with the Department of Criminal Justice, and Garcia had nearly 23 years. The inmates were serving sentences that ranged from one year for labeling unauthorized recordings to 20 years for drug possession with intent to distribute, according to online prison records.

Correctional officer Jason Self, 38, inmate Hector Rivera, 37, and 22-year-old inmates Terry Johnson and Damien Rodriguez were hospitalized in critical condition, the prison system said. Inmate Remigio Pineda, 34, was in serious condition.

The prisoners were being transported from the Middleton prison in Abilene to the Sanchez prison in El Paso, when the accident happened around 7:30 a.m. about 250 miles east of their destination.

Two containers at the back of the train were damaged in the collision, causing hundreds of parcels to drop along the trackside while the train ground to a halt, said Mark Davis, a railroad spokesman.

No Union Pacific employees were injured.

The train was traveling from the Los Angeles area to Marion, Arkansas.