Okay well, he passed a lie detector test, yay! But also anytime I've dealt with someone of that power, they have a way of tricking you. They always have a way of tricking you.
Also it should probably matter that he is - even if he says it's consensual - possessing the body of someone here. I'd think that helping that, especially if they were tricked into it via a pact or some other smarmy thing devils do, would be the number one priority.