AUSTIN -- Austin police Monday were trying to figure out how a man's body got on top of a moving train.

The case has investigators scratching their heads -- they say while they've seen cars and people hit while on the tracks, this is the first time they've found a body on top of a train.

It all started just after 7:30 a.m. A woman called 9-1-1 to say she thought she saw a man lying on top of a passing train. A short time later, two officers on an overpass also spotted the body.

The train was stopped in South Austin and APD, Austin firefighters, Union Pacific officials and the medical examiner arrived on the scene.

The victim is described as an Hispanic male, about 20 to 25 years old, wearing a black jacket, black jeans and white tennis shoes. He was carrying a blue and maroon backpack.

It's early in the investigation, but officers do have a theory about how he ended up on top of the moving train.

"The Hispanic male -- we believe the way the body is on top of the roof as well as the evidence that's there, we believe it's possible he could have jumped off an overpass onto the top of a train," Detective James Mason, APD.

The train was en route to Hearne, Texas, from San Antonio. The condition of the victim's body leads APD to believe the victim jumped onto the train somewhere in Austin.

If you have any information, or if you saw a young Hispanic man wearing black jeans, a black jacket on a train trestle or overpass, you're asked to call the Austin Police Department.

APD also wants to remind everyone that walking on the tracks or jumping onto trains is illegal.