He Said He Loved Her. Then He Went to the F.B.I.

John DiRubba turned informant to foil a murder-for-hire plot. Or was he just an ex-lover seeking revenge?

John DiRubba fell hard for Valerie Cincinelli. He can’t really explain it, just love at first sight. He was living in Queens, and she was a police officer assigned to the local precinct. One day while she was out on patrol she stopped when she saw him washing his car. They began to chat, and she told him she was married. “Not happily,” her partner shouted through the cruiser’s open window. Ms. Cincinelli, as it happened, was going through a contentious divorce.