Lauda admitted to trying to extort in order to get a confession or some further info about that person and his alleged scamming.
Partially correct. Lauda tried to extort someone who he believed had broken the law. It is common for extortionists to threaten to expose illegal activity if an extortion payment is not paid as a means to collect the extortion payment. Lauda later claimed he was conducting a "sting operation" however paying an extortion bounty would not establish guilt in any reasonable court of law, rather it would establish the victim was trying to avoid attention by law enforcement.
Now I don't see any evidence that an agreement was made before the attempt of extortion,
There is no one to make an agreement with. Lauda telling his friends about his plans to break the law (extort someone) in the near future does not give him a free pass to break the law, rather it most likely makes his friends co-conspirators depending on the exact details.
apparently there might be a pgp encrypted message, but gpg asks me for a secret key for that, but even then, you can't really prove it happened before the extortion unless they put a hash of that agreement in the extortion message and shared both of them after the fact.
The fact the encrypted message was submitted to a number of pastebin-type sites somewhat proves Lauda told his friends about the planned extortion attempt ahead of time, to the extent you trust the timestamps on those sites. However this presents many problems, mainly the fact that if the extortion attempt was successful, that no one would ever have found out about it because the message was encrypted to Lauda's GPG key only. Another issue is that telling his friends about his plans, makes his friends co-conspirators, and does not give Lauda a free pass to break the law.
The point remains that lauda remains as someone with authority within the forum, which has been explicitly allowed by theymos by way of keeping both blazed and hilariousandco trusted by the "default trust" account despite their keeping Lauda in the default trust network. As mentioned previously, theymos has previously explicitly directed that certain users not be included in the default trust network after leaving controversial ratings, and has declined to engage in this activity in this instance.
By way of the above, theymos is explicitly allowing an extortionist to remain in a position of authority.