Jack Noonan is a sergeant on the police force with Mary’s husband, Patrick. He is a respectful man who, though well-acquainted with the couple, always addresses Mary as “Mrs. Maloney” while she addresses him as “Jack.” He is one of the first pair of officers to arrive at Mary’s house after her desperate call to the station to report that she has just gotten home and believes her husband dead. She is comfortable enough with Jack to collapse into his arms in faux distress upon his arrival. He is kind and gentle with Mary and solicitous to her emotional needs in the midst of the crisis. He quickly determines that Patrick is not only dead but has, in fact, been murdered, though Jack has no idea he is familiar with the murderer. In fact, it may be this familiarity that leads him to relax some of his methods of scrutiny.

He is an experienced investigator and confident in his and his colleagues’ abilities to ferret out the truth. He puts the greatest weight in a homicide investigation on finding the weapon used for the killing. This proves to be a great irony in the story as Mary deceives and manipulates Jack and his fellow officers into unwittingly destroying the sought-after weapon completely, thereby getting away with her crime.