Would tenured professors who are charged with a crime generally be fired? What's the usual (North American) universities' practice on dealing with tenured professors who have been criminally charged?  I've encountered two scenarios indirectly that could make some professors in some legal trouble.

Here the first scenario.  When I was an undergraduate student, a colleague told me that his ex-girlfriend called because she discovered a stalker near her home.  When he visited her to assess the situation, they bumped into the alleged stalker at the stairs of the apartment building.  She asked him to call the police.  He recognized that the alleged stalker was one of the professors in his department.  He did not report the alleged stalker to the police because he's afraid of repercussion.

Fast forward a few years.  Here the second scenario.  One of my friends dated a tenured professor.  The relation was abusive.  He (the professor) hit her badly that she called the police.  His mom begged my friend not to press charges because she's concerned about her son's future.

TL;DR: In theory or practice, would universities fire the professor who have been criminally charged?  I've asked several tenured professors casually with at least one of the scenarios.  They all agreed that nothing bad would happened to those professors even if their wrongdoings were reported to the police.
Criminal acts are certainly a reason to revoke tenure.  In fact, this is probably one of the most common reasons.  It is possible to terminate the employment of a tenured professor as soon as the university learns that they have been charged with or suspected of a criminal action.  (This happened at my university: it was an extreme case.)  Terminating employment because of a criminal charge is obviously a quite precipitous act to take: I would be surprised if a university did this in any situation except one in which they are sure that the faculty member will/would be found guilty of the charge.  A tenured employee who was fired because of suspicion of criminal acts and was later found innocent of these acts would have, in many cases, a heck of a lawsuit against the university.  (Untenured employees might as well...)

The things that "you heard" sound a little dopey to me, honestly.  Tenure offers some measure of job security.  It does not confer any defense against or immunity from criminal acts.  Getting convicted of domestic violence is "something bad happening to the professor", right?  Not being able to carry out your duties because you are incarcerated is a sufficient reason to fire a tenured faculty member!  In the scenario with the "stalker" it is so unclear what happened or what was reported to whom that I would not be comfortable commenting on it.  Nevertheless, one can certainly imagine circumstances in which a tenured faculty member could be fired for stalking even without a criminal conviction.