I'll be sure not to piss any of you guys off. I like playing mind games with people...you see, fear is a powerful thing. If you leave a lot to thier own imagination, they just add to their own fear. Coming up with things in their head about who saw what, how many know, what else do they know about...it can really get to them.
But remember what a lot of other people have said here, be perpaired for the reaction to whatever you do. You might end up getting someone else fired. He might think that by getting rid of "such and such" whom he thinks is behind it, it will all go away. It is possible that other people could suffer as well.
If he is supposed to be a Christian and a family man, maybe he has a problem. Porn on the net...he shouldn't be doing this at work. But, maybe you could help him correct this by...sending him the tape, and with it include a little note. Jesus is watching you! That should wake him up! If this fails to yield the proper results, and you feel that more needs to be done then thats up to you.
I hope it all works out for the best, Good luck!
Jason