Most likely they were both in a processing area. It’s locked but it allows you to fingerprint the perp and take mugshots. Taking them in and out of a cell is a pain so you just secure the entire room. Perp is handcuffed until you need to fingerprint. Cop usually locks his gun in a locker before entering the room, and help is always just a yell away. Which is why the cops got there so quick once the perp started yelling and kicking the door.
That sounds a little more like it.
What is the status of the cop .. did he have a stroke or a heart attack ..??