Det. Packel is an NYPD homicide detective, probably working in one of Manhattan precincts (possibly Central Park Precinct.). He investigated the murder case of teenage girl Jill, which led to accusation of her boyfriend Clifford Danner.
Packel appeared in episode "Dog Fight" during appeal trial of New York v. Clifford Danner. Firstly, he seem to be irritated by opening his old case and doubting his investigation, but finally he helped Harvey and Mike to get Matt Bailey testify about Jason Black, who according to DNA analysis of victim's clothes actually committed murder. That resulted in vindication of innocent Clifford and accusation of Jason Black.