Before a gunman held up the OK Petroleum gas station on Montauk Highway in Brookhaven, police say he tried to rob a Valero station in East Patchogue.

The incidents happened about 30 minutes apart Sunday night, police say, and they suspect the same man in both.

Surveillance video obtained by News 12 shows the gunman aiming a pistol at two OK Petroleum employees and demanding cash around 9 p.m. The video shows him take a worker's cellphone and fistfuls of cash from the register.

Daniel Bolander, a store clerk, says the man asked, "You guys think this is a joke? Give me all the money."

Police say about 30 minutes earlier and about three miles away, the same man failed to get any cash from the Valero gas station, which is also on Montauk Highway.

"He had a gun, and he said, 'Give me the money,'" says Mohammad Waras, a worker there. 

But because the register didn't have much cash in it, Waras says the suspect took off empty-handed.

Kevin Beyer, of the Long Island Gasoline Retailers Association, says it's concerning that the robber struck a store with two employees on at the same time.

"You try to keep a couple of people on at a time so it helps with the security," Beyer says. "For them to come in anyway is pretty brazen."

Police are asking anyone with information on the incidents to contact Crime Stoppers at 1-888-220-TIPS.