As Rosa says, the murder didn't make it into the news, which she concludes means the police must have suppressed the news. (Me, I would have assumed it was because unexplained shootings aren't unusual enough in New York to merit media coverage.)
Hint 2
You now have the police department office where Durkin works on your map; let's go talk to him.
Hint 3
As it happens, he pretty much categorically refuses to pass on any information at all. Can we discover any information inside?
Hint 4
Well, Rosa can't, but Joey can. Send him on in (and enjoy hearing Rosa try to explain to Durkin why she's just standing in the snow for no particular reason).
Hint 5
Inside, go into the back room. You'll find what you need on the bulletin board.
Buy me a coffee