Mewtwo is NOT happy with Howard after the shit he's just had to go through!
Dissatisfied with how the human would get away with his attempt to not only control the psychic legendary but also to abuse his powers, Mewtwo came to the decision that he would deal with the scheming human here and now.
Enraged by how this event stirred memories of the past he endured under Giovanni's similar control, the psychic unceremoniously handled Howard with his psychic abilities to consume and digest the human alive! He would make the human suffer for his transgression, far more just than being arrested and sent to jail for whoever knows how long.