This is more than theft or lying. He needs to be taught about fundamental TRUST. Right now, you shouldn't trust him to do the right thing when nobody is watching. There's something deeper going on and you need to dig into it with a good man-to-man talk about hnor and values and what it really means to be a man. Respect for yourself and others if that needs to be articulated. In the meantime, mega-restriction on some of the freedoms that he has enjoyed over the years. Lock him down for a while - grounding, no electronics, nothing but homework and reading for at least two weeks. He earns your trust back then he earns the freedoms commensurate with that trust - and not until and certainly not all at once. Not to be dramatic, but if this isn't curtailed by Dad at age 11, it will be dealt with at age 16 by the Law. Find out why he feels the need to take from others. Is he not getting something basic in his life that the stealing helps to ease emotionally or is there more to it? Might take more than one talk, but in order for him to regain your trust, you need to convince him to communicate openly about his feelings.
Enjoy the ride up!