You use may with have to say that it is possible that something happened in the past, but you do not know whether it happened or not. Could have means that something was possible in the past, but it did not happen.
I would not 'take anybody out' on the basis of what I thought may have, might have or could have happened in the past as that's exactly what maniacs do. Surely we have justice systems for that sort of stuff or do you think you are Judge, jury and executioner?
There's a biblical proverb "Judge not lest ye be judged" for those who think they are, If you judge or condemn someone else you stand to be judged or condemned according to the same standard.