There seems to be a lot of confusion in here, so let me make at least this point clear:
The SEC is a civil enforcement agency, it does not have the power to bring criminal charges. That's why Shavers was never arrested for his actions related to his bitcoin investment scam. At the federal level, only the US Attorney's office can bring (non-military) criminal actions against an individual.
That's correct. And when the SEC finds criminal activity for which they think a fine isn't enough, they turn it over to the FBI and the US Attorney for prosecution. Wilmer Hale (a law firm) has a
list of SEC actions which include parallel criminal prosecutions.They don't do it that often. But, for example, Raj Rajaratnam of Galleon Management, a hedge fund, is now US Prisoner #62785-054, to be released in 2021.