A gas station and a 7-Eleven were robbed in Brookhaven Town within eight hours. Officers caught one suspect with the help of a security guard, Suffolk County police said Monday.

On Sunday, a man  wearing a red-and-black plastic mask and a green shirt used what appeared to be a handgun to hold up a Mobil station in Coram at 9:55 p.m.,  police said. He demanded cash from an employee at the Middle Country Road station, police said, and after the employee complied, ran off.

The suspect had a medium build, police said.

Sixth Precinct detectives ask that anyone with information on the robbery call them at 631-854-8652 or call anonymously to Crime Stoppers at 800-220-TIPS.

The second robbery occurred about 6:05 a.m. Monday when  a man pretended to make a purchase at the 7-Eleven on Broadway Avenue in Holbrook, then grabbed money from the cash register when the employee opened it, police said.

 The employee tried to stop  the man and the two struggled before the robber broke free from her and drove away, police said.

However, an off-duty security guard was getting coffee at the store, and upon seeing the commotion, jumped into his car and tailed the robber, police said.

He helped direct officers to the suspect's location, and officers arrested Kevin Chieffo, 42,  a short distance from the store, police said.

The employee was not injured, police said.

Police booked Chieffo, of North Dunton Avenue in East Patchogue, with third-degree robbery and held him overnight to be arraigned Tuesday at First District Court in Central Islip.

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