Video shows armed man in attempted Subway restaurant robbery on Longwood Avenue

Cops have released surveillance video in their search for an attempted robbery suspect. 
According to police, an armed man was caught on camera walking into a Subway restaurant on Longwood Avenue on Saturday. 
They say he then pulled out a gun and demanded money, but ran away empty-handed. 
He's described as being Hispanic, and about 5 feet 8 inches tall with a black beard and short black hair.