The Beneficiary (1997)

A man and woman detective team investigate the murder of a corporate president, but because the deceased was a friend of the male detective, he is reluctant to believe the signs that point to the widow as the killer. Still, the team take turns watching her movements, but during the male detective's turn, his past friendship with the deceased gradually allows him access to the suspected widow, and it isn't long before they're in bed together. But when he discovers that she's the beneficiary to millions that had been meant for her husband, the detective is moved in ways quite unpredictable.