The Ice Man Ben Kehoe in first film 48 Hrs.
As Nick says hes been after the Ice man for years, so what did the Ice Man do in the first film? Murphy stole the money from the Iceman before the first film. so the Iceman was obviously the Iceman back in the first film.
The second film Another 48 Hrs is set what seems to be 5 or more years after the first film, and Nolte says he has been on the case for 4 years, Ben Kehoe from 48 Hrs and Another 48 Hrs was revealed to be the Ice Man killer that was behind the events of both movies.
Kehoe even mockingly tells Cates that he is not his answering service when Cates finds out that Reggie called him from that Black club earlier and laughs mockingly about that, one hint of his bad nature early on, he uses Reggie and the Ganz Brothers to get the money for him, and probably Billy Bear, that probably why Reggie was let out because he could get the money for him.
Kehoe plays an honest cop in this movie but in the sequel he was so horrible and had been dirty all along, sucks for everyone but you can see he is hiding stuff in that scene where he didnt tell Cates that Reggie called right away.