"Many abusive priests, like the one above, have voluntarily left or been removed from the priesthood, which begs the question, who is monitoring them now?"
It doesn't "beg the question".  It may "provoke the question" but it certainly does not endure a conclusion-yet-to-be-drawn as a premise of the argument.
Now that that's out of my system...
If the former priest was removed or resigned from ministry on evidence of abuse (not simple accusations), a diocese has a duty to ensure the safety of the public if a criminal trial could not be completed due to SoL.  These should not have been laicized, IMO, or allowed to resign, but sent to an island (or other place of isolation) to live out the remainder or their lives.