Blood Groups

I realise that this is most probably a stupid question (as I wasn't really giving this film my full attention admittedly) but how does the killer know the blood type of Clint Eastwood's character as well as those of the man at the ATM & the lady in the grocery store? From what I can remember he didn't work at the hospital & therefore would not have had access to confidential files........
PS-I didn't really think this film was up to much anyway-Is it worth a second viewing where I give it my undivided attention next time?! :o)