New Hampshire State Police are investigating a robbery at the Hooksett Toll Plaza on Interstate 93. Police say a man approached the toll booth on foot just after 1 a.m. Monday, displayed a handgun, and took an undisclosed amount of cash. The toll attendant was not hurt. Police say the robber fled on foot. A search of the area, which included a State Police dog, failed to find the suspect. The robber was described as a white male of medium build who was wearing a black plastic face mask, shorts, and a dark-colored T-shirt.