Out of the Game by David DeLee

Still struggling to come to terms with the loss of his family, former- DEA Agent Nick Lafferty gets drawn into a case when ADA Caitlin McKenna requests his help investigating the killing of two cops and her key witness in a murder trial.

Accused of murder, being investigated by the FBI, and out of options, Lafferty re-teams with his ex-partner and soon-to-be ex-cop, Delmar Harley, a man wrestling with his own demons.

As they set to square off against the notorious Cosa Nostra, Lafferty prepares for the worst. But the deeper he digs, the more dangerous things become,
and before long, more bodies begin to drop.