COMMERCE CITY, Colo. -- A 17-year-old high school student suffered severe injuries to one of his legs after he was run over by a Union Pacific train Tuesday morning.

Police said the victim was one of four Adams City High School students running near the train at 69th Avenue and Elm Street at about 7:20 a.m. The victim, identified as Jon Pounds, slipped on the tracks and was hit by the train.

"There was a slow moving train going southbound. From what witnesses told us, he tried to climb through two of the cars as it was slow-moving," said Chuck Saunier, with the Commerce City Police Department. "At that point, I don't know if he tripped, if he fell or something got caught up. But it sounds like he went under the train."

The three other students were not injured but were offered and given counseling when they arrived at school. The train crossing is about 200 yards from Adams City High School.

Richard Montoya was sitting in his car, waiting for the train to cross when he heard Pounds scream.

"I could just hear screaming, 'I'm in pain!' And I called an ambulance and told them, 'You need to get here right away,'" Montoya said.

Montoya ran to the victim and saw that the victim's leg was badly mangled and may have been partially amputated.

"It was just horrible to watch. There was nothing I could do. I was just stunned by it," Montoya said, tearing up. "My heart goes out to the family if he has to amputate his leg. I feel sorry for him. I really do."

Montoya said it was the most traumatic thing he had ever seen in his life.

Pounds was transported by ambulance to Children's Hospital in Denver.

The mishap is under investigation.

Railroad officials, who have already been out to the scene to investigate, said that the crossing signals were working properly and according to equipment that measures the speed of a train at that particular crossing, the train was moving at about 26 mph.

A student who goes to school with the victim described him as a "bit of a daredevil." He played football for the school, she said.