(CBS) — It is a disturbing scene: an abandoned building where a longtime community activist and crime fighter says teenage girls were held against their will and forced into prostitution.

CBS 2’s Jim Williams reports from Gage Park.

Andrew Holmes is at many crime scenes but he’s especially passionate about this.

He says teenage girls — runaways — were held captive and forced by pimps to have sex.

How did he discover it? Holmes works for Morrison Investigations, a private detective agency. They got a tip about illegal activity that Holmes says points to human trafficking.

The agency did surveillance, and Holmes says last January he spotted a young girl dropped off at the abandoned building near 63rd and Kedzie.

Holmes says by the time he walked through the other girls were gone.

The building owner, James Zar-Hall, says he had no idea it was happening, though he insists he checked the property at least once a month.

“You can’t be somewhere 24/7,” he tells Williams.

Zar-Hall was working to make the building more secure.

Holmes says the one girl was returned to her mother. No arrests have been made. Chicago police tell us they have no reports of such activity at the building but are reaching out to Holmes for more information.