Sounds like he got himself banned. The thought is if you let people who have been banned still post but auto kill them, then spammers will not try to work around their ban. Your co worker can try to contact PG and crew to get himself unbanned or just create a new account. Note you can turn on show dead to see what has been killed in this manner.

Thanks for your answer. Do you have any idea where he can contact the crew and PG? Any email addresses?

that's possibly because he has too low karma like me :) understand how it works better here: http://news.ycombinator.com/item?id=196509