The suspect first tried to rob a gas station in East Patchogue last week.
After the clerk refused to hand over any money, the suspect tried another gas station in Brookhaven.
The armed robber cleaned out the register and took off.
Police are offering a $5,000 reward for information leading to an arrest.
----------
* More Long Island news
* Send us a news tip
* Download the abc7NY app for breaking news alerts