You have to make sure you haven't stepped over the line into entrapment.
Vigilantism is illegal. Assault is illegal. If you use any weapon to "beat the thief", you can upgrade that to assault with a deadly weapon and possibly attempted murder. And since you set up this little "sting", it's premeditated.
And if you somehow manage to survive all the criminal charges against you, the "thief" will sue you in civil court for everything that you own. You'll either end up giving it to them or spending it all on an attorney... and you still may have to give a bunch of your stuff to them.