REVERE – Revere police are investigating yet another knifepoint robbery. This time officers were called to Hess gas station at 630 Squire Road shortly before 11:30 p.m. Monday.It’s the fourth armed robbery reported in the city in less than one week.According to a police report, the suspect walked into the Hess bathroom and exited holding a folding knife in his hand.The suspect demanded money but the store clerk hesitated, thinking the robbery was a joke. The suspect then walked around the counter and continued pointing the knife at the employee, who then gave him an undisclosed amount of cash.The thief, who was wearing a hooded sweatshirt tightly around his face, fled the store on foot. Police only described him as a 5-foot-8 white male.Within 24 hours on Saturday, two street robberies were committed by similar-looking suspects on the same two-block stretch of North Shore Road near Shirley Avenue.”The detectives are looking for a link between the armed robberies,” Police Capt. Michael Murphy said. “Currently, they are not able to link the two street robberies to the Hess gas station event.”Last Thursday about 10:30 a.m., a man burst into Tobie’s Jewelry Store on Shirley Avenue waiving a gun before fleeing with cash and cheap rings.No arrests have been made in any of the robberies.