from northern iraq, special correspondent marcia biggs, and videographer alessandro pavone report. a warning: images and accounts in this story may disturb some viewers. >> reporter: it starts at dawn here in west mosul. members of iraqi special forces, going door to door in search of isis sleeper cells. clashes continue in a small pocket of the old city, but for most of mosul, this is where the fight against isis stands. in some houses, we find the remnants of life under isis. "this was a daesh prison," he says. so this was once the home of a local politician. when isis took the area, they turned his house into a jail. "isis put in prison anyone who didn't pledge loyalty to them, who didn't join them and stick to their rules," this lieutenant says. "they considered them outlaws." after several hours searching, they come across this man, who they believe may have escaped the current clashes in the old city. he is arrested immediately. do you believe he is an isis fighter? >> ( translated ): i think he is. he is not from this area, no one has ever seen him here. people here don't kn