Three local police departments — Groton, New London and Stonington — are working together to determine if two robberies and one attempted robbery, all of which have happened since Thursday, are related.

After waiting for customers to leave the store, a man attempted an armed robbery at the Sunoco gas station at 715 Colman St. in New London shortly before 8 p.m. Saturday, police said.

The man approached the clerk, displayed a handgun and demanded money, but was unable to obtain any cash, according to a New London Police press release. He then fled the store on foot, police said.

Police said the suspect is a white male, with an unshaven face, who was wearing a dark hooded sweatshirt, yellow gloves and sunglasses at the time of the incident.

Just before 9 p.m. Saturday, Stonington Police Capt. Todd Olson said, a man robbed the Henny Penny store at 2 Roosevelt Ave. in Mystic.

Olson said the man — described as a white male wearing a black sweatshirt — got an undisclosed amount of money, but did not display a weapon.

After the man fled on foot, Olson said, Groton Town Police, Connecticut State Police and Amtrak Police worked with the Stonington Police to attempt to track him.

The case is under investigation.

Around 8 p.m. on Thursday, a man entered the Henny Penny at Route 12 and Tollgate Road in Groton, displayed a handgun and demanded money from the store clerk, according to Groton Town Police. He then fled the store on foot with an undisclosed amount of cash, police said.

A Groton Town Police press release described the suspect as a heavy-set white male — with facial hair and a gap between his teeth — who was wearing a dark hooded sweatshirt, gray pants, sunglasses and yellow work gloves at the time of the incident.

"We're currently working with the New London and Groton police departments to verify or see if we're looking at the same person," Olson said.

New London Police are asking anyone with information about the case to contact them at 860-447-5281.