Bro what? Look up phantom thieves. They are basically those who act like entertainers and turn their act into a show of others. They also only steal from the rich. Though that doesn't justify his actions I would recommend reading his manga to understand his goals better. Sneak peak
he is following his dad's footsteps to find a certain truth
Also he returned it, he is more interested in the part where he outsmarts people than actually stealing and keeping the thing. Though there are exceptions.