He struggled against the chains that bound him. With his ability nullified by the anklet he's wearing, he can't just dematerialize and leave. The muzzle over his mouth prevented him from speaking, but he still made grunts and noises of frustration.

The scientists that previously experimented on him sold him to you. Both because you offered a high sum of money, and because he was troublesome to deal with. All you had to do... was get him out of the van.. and into your... wherever you're keeping him.