DENVER -- Investigators believe a man crossing the street in downtown Denver Wednesday night was hit not once, but twice by passing drivers before he died and witnesses say that the second vehicle that struck him was an ambulance.

The 52-year-old man, whose identity has not been released, was pronounced dead at the scene.

Eyewitnesses say that the man was crossing Colfax Avenue near Lipan around 7 p.m. when a Jeep Cherokee struck him, causing him to fall to the ground. He was then struck by a second vehicle that fled the scene, a vehicle described as a white ambulance with red and blue paint, witnesses said.

"The company that best fit the description given by witnesses was American Medical Response and AMR management was extremely cooperative with investigators," Denver police said.

AMR had all of their ambulances that may have had been in that area at the time of the accident respond back to the scene for a vehicle inspection. Investigators tentatively identified the ambulance involved in the accident from physical evidence discovered on the undercarriage of the vehicle.

The driver and passenger of the ambulance were questioned and released late Wednesday evening.

Investigators are still trying to determine if any charges will be filed.