Bomber's Law — George V. Higgins

Bob Brennan is an old-school Boston cop who knows a lot about Short Joey Mossi, a mob hit man who's neatly taken care of at least eleven competitors. In fact, as Harry Dell'Appa, a hotshot detective recalled from banishment in the sticks, discovers, Brennan not only knows a lot, but he talks a lot, too-about who Joey's killed, and about how and why. So why won't Brennan bring Joey in? That's what Harry has to find out.