MIAMI -- Police say a security camera caught a registered sex offender preying on a girl at a South Florida store. It allegedly happened at the Sears on Coral Way and 37th Avenue in Miami.

Authorities say the tape shows the 40-year-old man suspect circling a group of girls as they are shopping for merchandise. He looks around to see if anyone is looking, and then grabs one of them in the buttocks.

Police say there is a lesson for parents and children in this assault. They say that usually victims aren't aware they are being assaulted because they think someone has simply bumped into them.

In this case authorities credit a security worker for being very alert while watching security monitors, zooming in to the suspect, and catching him during the alleged assault.