A worker at a Mineola Dunkin’ Donuts helped cops apprehend an armed robber who stole about $400 Saturday afternoon, police said Monday.

The robbery occurred shortly before 5 p.m. at the Dunkin’ Donuts at 120 Old Country Rd. — across the street from the Nassau County courthouse, an area bustling on weekdays with armed police officers and court officers — when Phillip Robinson, 52, of South Franklin Street, walked in with a black handgun and demanded money, police said.

The cashier, 20, complied and police said Robinson fled in a gold-colored vehicle with an undetermined amount of money.

But not before the suspect took out a rag and wiped down the register, in an apparent attempt to get rid of any fingerprints he might have left as he pilfered the cash, according to another employee, a shift supervisor, who helped cops make the arrest. A store manager said the thief got away with $410.

The shift supervisor, who didn’t want his name published, was in the parking lot on his break and saw the suspect running from the store, he said. He went back inside the store and the cashier told him: “He took the money and he ran away.”

The shift supervisor, 45, ran after the suspect, who he saw jump into a gold-colored vehicle. He saw the vehicle traveling on Old Country Road and hopped into his own car and followed the suspect to get his license plate, he said.

The suspect drove south on South Franklin Avenue — right past Nassau police headquarters — into Hempstead. The worker got the suspect’s plate number and then went back to the store and gave it to First Precinct officers, who arrested the suspect in less than an hour in Hempstead, police said.

Nassau Det. Vincent Garcia, a department spokesman, confirmed the shift supervisor’s account of his role: “Witness was able to provide pertinent information with regard to the vehicle, direction of travel and license plate information.”

Garcia called the worker’s decision to stop following the suspect “a very wise and prudent choice.” The police department generally advises civilians not to follow armed suspects.

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Robinson was charged with robbery, criminal use of a firearm and criminal possession of a weapon. He was ordered held without bail at his arraignment Sunday at First District Court in Hempstead, according to online court records. He’s being represented by a Legal Aid Society attorney, records show.

The shift supervisor finished his shift on Saturday and was back at work on Monday, making iced coffees and bagging doughnuts. A five-year-employee, he said he was not at all anxious after the robbery.

“I told my wife and she said, ‘Why did you do that? It’s dangerous,’ ” he said. “I told her, ‘What can I do? In front of me, someone was cheating.’ ”