Calgary homicide detectives are looking for a young woman after a 17-year-old boy was likely shoved off a downtown train platform, then died as a C-train lumbered to a halt.

Crowds of rush-hour commuters watched in horror Wednesday as the teen, who was apparently embroiled in an argument with the woman, fell off the 8th Street Southwest station platform.

Calgary police investigate at the downtown LRT station Tuesday evening.
(CBC)

More than 100 people were on the above-ground downtown Calgary Light Rail Transit platform when the teen died at about 5 p.m.

Police, initially reluctant to say the fall was intentionally caused, confirmed Thursday that Gage Jeffery Prevost of Calgary was likely pushed and slipped into the gap between two train cars. He died instantly of massive internal injuries.

After interviewing 15 witnesses and reviewing surveillance video, police had no one in custody, but were looking for a female suspect, said Staff Sgt. Kevin Forsen.

"The suspect in this case is described as a dark-skinned, possibly aboriginal, woman in her mid-20s with facial scarring. The woman was wearing tight-fitting, capri-style pants and a red or pink tank top."

Forsen said police don't know if the two knew each other before the argument on the platform.

Witness Chanelle Carson said she saw "people shoving and pushing."

"And then a bunch of people yelled and then we heard this loud sound, like a grinding-thumping, and then everybody started screaming and running."

Police said Prevost was in a "physical altercation" with the woman before his fall.

"It was a fight, for a lack of a better word," Duty Insp. Keith Pollock said when asked what happened moments before the fatality.

Officers took two females spotted running from the scene into custody and questioned them Wednesday night. A third female was also interviewed by police.

Forsen asked anyone with information to contact police.