Nassau police Tuesday released a sketch of a suspect wanted in a string of unsolved gas station robberies.

The suspect has used a black semiautomatic handgun during the robberies and he "consistently" covers the weapon with a T-shirt or cloth.

The suspect is believed to be in his 20s, about 5 feet, 8 inches tall with a medium build. He has worn a white hat during some of the robberies.

Police said the robberies occurred in Hempstead, Baldwin, Franklin Square, Valley Stream and Elmont -- all in August.

They are as follows:

The BP station on Peninsula Boulevard, Hempstead, on Aug. 4 at 10:10 p.m.

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The Mobil station on Grand Avenue, Baldwin, on Aug. 11 at 11:05 p.m.

The Star station on Hempstead Turnpike, Franklin Square, on Aug. 11 at 11:32 p.m.

The BP station on Merrick Road, Valley Stream, on Aug. 12 at 11:45 p.m.

The Citgo station on Hempstead Turnpike, Elmont, at about 11:20 p.m. on Aug. 18.

No one was injured in any of the robberies.

Police are asking anyone with information to call Crime Stoppers at 800-244-8477. All calls will remain confidential.