The next few seconds have someone in the building open fire with short bursts before stopping.

Bart has one of his dogs sent into the dark building, noticeably skeptical. The dog stays low, and sniffs around the lobby.

Sean goes in after the canine, peeking around the corner. He sees no-one, dead or alive, lurking there. The shots must have come from somewhere else...

Sean notices the dog has picked up a scent. The good boy makes a low growl and comes over to him, nudging him with his nose to alert him to something. Sean follows the dog's hint and realizes the dog has detected people behind the counters with glass dividers.