Thanks, Monica.  I met O'Toole a few times "back in the day." He was the archivist for the Archdiocese of Boston when he undertook the biography of O'Connell as his doctoral dissertation. Before he began, O'Toole said he asked Cardinal Law if he would have unimpeded access to the material he needed, and freedom to write candidly. Law assured him that he would, asking only that he tell the story truthfully. Law kept his word, and so did O'Toole.
If you haven't read Slawson, I recommend his book. It focuses more specifically on O'Connell's defects, but it is well-sourced and provides important insights, I think, about the depth and breadth of the corruption in the Archdiocese.
So, Law thought he inherited a problem ...?? 
There's a tradition for that, too. O'Connell directed the authors of a three-volume history of the Archdiocese to portray his predecessor, John Williams, as bumbling and incompetent (he wasn't) and O'Connell as the savior of the diocese (he definitely wasn't!)