Why'd Frank leave a card on Billy's mom's grave at beginning of movie?
http://i.imgur.com/oclfIyQ.jpg
I didn't think they had anything to do with each other at that point in the movie and it wasn't 'till later they knew anything about each other/they became intertwined. The only thing I can think of is that Costello and his outfit knew about the Costigan family in general with Uncle Jackie, Bill's uncle, as well as his father who worked at the airport, lol, and had respect for them to a degree because I know they spoke positively of Uncle Jackie. Any ideas, guys?