MAN WHO CHEATED HIMSELF, THE(1950)
In the set: 100 Greatest Mystery Classics

A police detective gets involved with a married
brat(Wyatt)! She kills her husband while he is
there and he starts a cover-up to get her out
of trouble! Problem is, his brother is also a
detective, and he won't give up til he finds
the truth! Wyatt(Star Trek: TOS episode "Journey
To Babel", Star Trek IV "The Voyage Home", Father
Knows Best) is just not cut out to be a bad girl! B-

A review from IMDb.com:

Despite Jane Wyatt, who offers possibly the worst
performance of a femme fatale in the whole noir
cycle, The Man Who Cheated Himself is a
more-than-passable, gritty little thriller.
Veteran cop Lee J. Cobb is showing the ropes
to little brother John Dall ("Gun Crazy," "Rope").
Dall is on the verge of blissful matrimony but
Cobb still likes to play the field, the field
being filthy-rich society matron Wyatt. When
she kills her ne'er-do-well hubby (by accident?
It's never clear), Cobb helps her cover up the
crime. Trouble is, he taught his brother the
tricks of the trade rather too well... This
movie is rather better than you might expect
it to be, thanks to Cobb's moaning, double-bass
voice and some not-terribly-stale plot
developments. - bmacv