The National Transportation Safety Board is investigating the circumstances of a deadly train collision Oct. 4 that occurred about 18 miles west of Cheyenne.

Two Union Pacific Railroad workers were killed that night when a train headed east from Pocatello to North Platte collided with another train parked on the same track, officials said.

Railroad officials identified the victims as Jason Martinez, a 12-year railroad worker, and Benjamin Brozovich, a railroad conductor with 20 years of experience.

Officials said Brozovich’s body was recovered that night, but Martinez’s body wasn’t found until Saturday.

NTSB spokesman Terry Williams said both of the deceased railroad workers were aboard the moving train, which was hauling mixed freight when it hit the rear of the train that was stopped.

The crew of the stopped train, which was traveling from Green River to Cheyenne, had evacuated prior to the collision, Union Pacific spokeswoman Raquel Espinoza said. NTSB is investigating why the train had stopped, or why the other crew was unaware of the hazard.

On the night of the collision, Union Pacific officials estimated 56 train cars were derailed. Lt. Don Hollingshead, of the Laramie County Sheriff’s Office, said deputies were dispatched to the scene at 7:40 p.m.

Two crew members from the stopped locomotive went to a local hospital for post-accident screening but were not treated for injuries, Hollingshead said.

Both trains were equipped with event recorders, which took video and recorded the speed of the moving train, Williams said. He said the recorder onboard the moving train was damaged and had to be sent to the manufacturer for data recovery. The other recorder has been sent to the NTSB headquarters in Washington, D.C., where the data will be evaluated.

Williams said the recorders should clarify whether or not the moving train sounded a horn, or deployed its breaks.

Four NTSB investigators were sent to the scene on Friday.

“We’re in the very, very early stages of this investigation — the fact-gathering phase,” Williams said.

Williams said the investigation will likely take up to a year and a half to conduct.

It will move to an analysis phase before the board will make a determination of probable cause and issue recommendations to avoid similar accidents in the future.

Exit 345 (Warren Road) on Interstate 80 was closed, as well as the truck parking area at that interchange. The Interstate 80 Service Road eastbound at Exit 342 (Harriman Road) was also closed, though traffic accessing the quarries in that area was allowed, according to a Wyoming Department of Transportation news release.

Immediately following the crash, first-responders assessed all of the train cars and found no immediate hazards or threats to the public, according to a Cheyenne Fire and Rescue news release.

Cheyenne Mayor Marian Orr said she had been in communication with first-responders, as well as Union Pacific officials.

“This was a significant and tragic event. We are a community of railroaders, and tonight our community has experienced loss. And if you pray, please pray,” Orr said.

Responding agencies included Cheyenne Fire and Rescue; F.E. Warren Air Force Base; Laramie County Sheriff’s Department; American Medical Response (AMR) ambulance; Laramie County Fire Districts 1, 2 and 10; Cheyenne-Laramie County Health Department and Wyoming Highway Patrol.