Well, you'd be amazed at how many thousands of people who post on this site say they have proof. Then when they explain what they have it turns out not to be proof.
Hence the question as to what your proof is.
I can't address your other questions without knowing that.
Except for the last question.
amesjay:We just want to be sure that if we take this
risk and pay him, will he guarantee us that
we will win this case?
No, he won't. No lawyer anywhere can ever "guarantee" that you'll win the case.