The Man Who Cast Two Shadows

Description for THE MAN WHO CAST TWO SHADOWS by Carol O'Connell:

Formerly a child of the streets, now a brilliant computer hacker and NYPD sergeant, Kathleen Mallory's powerful intelligence is matched only by the ferocity with which she pursues her own unpredictable vision of right and wrong. And she will need every bit of that intensity now, in a murder case that strikes close to home in more ways than one...

This is #2 in Kathleen Mallory Series.