(adsbygoogle = window.adsbygoogle || []).push({}); The best way to kill the Pentagon Theif is to do the Table glitch on FIVE.
Once you are there you will find the Pentagon Theif running after you.
While you are on the table, he will run against the chair or table.
While hes doing that you can shoot him the the head .
Or if you run out of amo, lie down and crawl over to him slowly untill you can knife him.
Either way this will get you the trophy.

I have not seen this way to kill him on the forums yet.
Its a bit obvious but just posted incase people where still having trouble.

Making video soon will update, easy enough to do/read from.
Good luck and peace out