Sheriff Ross Mirkarimi may be guilty of domestic violence, and if he is -- as I've said  repeatedly  -- it's a serious crime and he should be held accountable. It will be very hard for him to remain in office with a DV conviction, even if it's just a misdemeanor.
But right now, the charges are just that -- charges. In the eyes of the law, he's innocent until proven guilty. So I don't see how Mayor Ed Lee can suspend him. 
Lee's under a lot of pressure, and under the City Charter, he has the sole authority to suspend an office holder for "official misconduct," which is defined as "wrongful behavior by a public officer in relation to the duties of his or her office." If there's a suspension, the Ethics Commission and the Board of Supervisors would both have to vote to remove Mirkarimi permanently.
But here's the thing: Lee has no evidence of official misconduct -- not unless the district attorney decides to turn over to the mayor all of the files in the criminal case, at which point Ethics and the supes would be holding mini trials of their own on evidence that hasn't been adjudicated in court (and a court may rule some of it inadmissable).
That doesn't seem likely (and it would be very odd for the D.A. to join the mayor in what would amount to a second prosecution).
And all of this would be going on at a time when the actual criminal trial is only four weeks away.
The courts have interpreted "official misconduct" fairly narrowly. If Mirkarimi is convicted, then the city attorney can get into the argument over whether domestic violence has any "relation to the duties" of the Sheriff's Office, and since he's a law-enforcement officer, that might not be too hard to argue. Certainly the charge of influencing a witness would be subject to that interpretation. So after a conviction, Lee would be in a position to think seriously about suspension -- if Mirkarmi didn't step down on his own.
But right now, there's no conviction. In terms of the court system (that would have to get involved) Mirkarimi isn't guilty of anything yet.
Mirkarimi could decide to take a leave of absence, although he doesn't seem inclined to do that. But whatever the merits of the case, and whatever the political arguments about whether the sheriff can do his job in the middle of this media circus, I -- admittedly as a nonlawyer -- can't see how Lee could possibly invoke the suspension provisions of the Charter.
Maybe I'm missing something.