The way I see it, "the five dead, two of them cops" adds up:
1.) Wuertz (Cop)
2.) Sal Maroni's Passenger (and if you argue that he only knocked the passenger unconscious, we can assume Dent murdered the bartender that served Wuertz (off-screen)).
3.) Sal Maroni's driver
4.) Sal Maroni himself
5.) Detective Ramirez (COP) (Again, Ramirez was NOT killed. The GCPD, however, have reason to believe that she was murdered since she was nowhere to be found. Dent specifically targeted Wuertz and Ramirez during the early rooftop scene, so Gordon could have assumed Dent got Ramirez after he finished Wuertz. This one's a bit vague but really it's the only plausible assumption IMO.)
I'd definitely like to see the issue come up in TDKR though.