McAllen police have asked for the community's help finding the so-called "polite robber."
Surveillance video at a Stripes convenience store showed a man talking to the cashier, then showing a knife and demanding money.
He headed behind the counter and grabbed the money.
But before he left, he asked the cashier not to call police and wished her a good night.
The suspect is in his mid-20's, has a thin build, with short black hair, a thin mustache and a goatee.
If you know who the man is, call McAllen Ccrime Stoppers at (956) 687-TIPS.