Chill of Night by John Lutz

The excerpts focus on a massive manhunt for a serial killer dubbed the Justice Killer, who targets former jury forepersons and jurors responsible for acquitting seemingly guilty defendants. The investigation is spearheaded by Captain Beam, a detective recently brought out of retirement after his wife's suicide, who grapples with his own personal issues and a growing relationship with Nola, the widow of an informant he failed to protect. As the case progresses, the team, including detectives Nell and Looper, tracks the killer’s actions, including the murder of juror Tina Flitt and jury foreman Carl Dudman, noting the killer’s meticulous planning and the consistent use of the letter "J" left at the scenes. Ultimately, the investigation reveals the surprising identity of the Justice Killer to be Deputy Chief da Vinci, who was driven to vigilante murder after his wife's suicide following the acquittal of their son's killer, bringing the dramatic and personal case to a violent close.