The incident occurred at approximately 3:10 a.m. on Thursday, May 25 at the West Hempstead Mobil gas station at 579 Hempstead Turnpike.
A man entered the gas station, took more than $300 and cigarette packs from the cash register, and fled the scene, police said.
It is unclear whether he fled on foot or in a vehicle, or in which direction he fled.
The burglar is described as an adult male wearing a blue mask, gloves, a dark hoodie and yellow pants with black stripes.
Anyone with information regarding the theft is encouraged to contact the Nassau County Crime Stoppers at 1-800-244-TIPS.
All calls will remain anonymous.
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