DOC does do a pretty thorough background check- much more thorough than 30 years ago when it was pretty much limited to checking for a criminal record. Also the interview process has been refined to elicit answers that might indicate if there is a problem. Nevertheless even with the most rigorous checks wrong folks will be hired at times- I remember when NASA had some astronauts get involved in some nutty love triangle where one was ready to hurt another- or Secret Service agents routinely compromising themselves with prostitutes when on Presidential details. I'm sure both these organizations do far more thorough checks than most all Police and Correctional Departments could afford. Happily in the case of Alvarez fellow staff stepped up and reported the misconduct and management acted in a responsive manner to deal with the problem.