For the fourth time over a month and a half, a gas station in Fairfield has been robbed.

Police say a suspect wearing a ski mask entered the Mobil store on Stratfield Road around 9 p.m. Sunday, pulling out a knife and demanding money from a clerk before running off.

The suspect got into a light gray, older model Chevy Silverado with a ladder rack affixed to the top, according to police. There was also a tool box in the bed of the truck. 

Police say that a witness provided a detailed description of the car and followed the suspect to a condo complex.

"This witness was very key in our investigation," says Sgt. Michael Paris, of the Fairfield Police Department.

Police chased a vehicle matching the vehicle description on Park Avenue in Bridgeport, but lost it.

The string of robberies has caused some drivers to change their gas routine.

"I would do it early in the morning when there's a little bit more traffic.  In the evenings, I know traffic is slow at some of these service stations," says Ovi Rosario, of Bridgeport.

Officials tell News 12 that the gas station was the scene of a robbery last week. A gas station on Jennings Road was also robbed.

Anyone with information is asked to call police.