...because of these reasons, was there ever an attempt of investigation on Theymos, Cyrus and other old and famous bitcointalk members?
You forgot sirius. He was the Bitcointalk administrator before theymos. Theymos made his way up the ladder to get to where he is now. He was a Global Moderator and then he became an admin when he was needed.
The story of how I became head admin is actually pretty boring. Moderators were needed, so I was made a global moderator. Then admins were needed, so I was made an admin. Then over time the other admins slowly lost interest and resigned until I was the only one left. I guess most of the people who were around here to see this have more-or-less left the community now. That's a bit sad.
It's not entirely clear, but for simplicity I usually say that I became head admin at the beginning of 2011, a little over a year after the forum was created.
The forum was originally located at bitcoin.org/smf, then forum.bitcoin.org (hence the redirect), and finally bitcointalk.org. Fun fact: The name "bitcointalk" was invented by Jeff Garzik, and he's the one who bought the domain.
You might also want to read this
interesting interview with sirius. Satoshi knew how to cover his tracks, so even if one of these guys is satoshi, they would know how to cover theirs as well.