Replying to spy work

my parents own a tool and die shop and things have been dissapearing lately including a laptop, a tv, a car radio (this guy had his car inside in some empty space in the shop to work on it) and like $1000+ worth of aluminum and my mom is convinced its this one guy but we cant pin it on him, they tried using a hidden camera but it got ripped off too, i guess it well hidden, anyways my mom is trying to think of a foolproof way to get this guy and im not coming up with anything, any suggestions