There's a developing story here as the SFPD is reportedly investigating some surveillance footage picked up at the foot of the Stockton Tunnel near Union Square that shows two male suspects violently dragging a woman out of the tunnel and into a waiting vehicle.

The footage was posted by KPIX's Joe Vasquez on Facebook, and it's not clear when this assault and possible kidnapping took place. "The origins of the video are unknown but a police source tells me they are being inundated with messages and calls, and my source confirms it happened recently near Union Square."

Vasquez's description suggests that this was not picked up by the network of 18 high-definition surveillance cameras in and around Chinatown that were installed by the city just last year following a spate of crime in the neighborhood. But was this Nest cam footage?

This story is developing.