The attempted robbery happened April 1 around 2:30 a.m. at a gas station in the 9000 block of the North Freeway.
According to police, the suspect walked into the store with a bag, pulled a rifle out and demanded money from the clerk.
Police said the suspect pulled out what was believed to be an AR-15 with a scope, pointed it at the clerk, and then stuck the rifle's barrel through the cash slot. He became frustrated, though, because it appeared he did not know how to operate it.
"Lack of experience with assault rifle frustrates clumsy robber as he flees empty handed," police wrote on Twitter.
The suspect then fled the store in a dark colored sport utility vehicle, according to HPD.
The suspect, is described as a black man between 25 to 30 years old, he's 6'0" and weighs between 220 to 250 pounds. At the time of the robbery, he wore dark black clothing.
Anyone with information is asked to call Crime Stoppers at 713-222-TIPS (8477).