ST. PETERSBURG — A worker was killed Thursday after he was pinned under a large piece of equipment at a jobsite near Sawgrass Lake Park.The accident occurred about 3:45 p.m. as John Winchester, 53, of Palmetto, was driving a roller on the top of a sand berm. The company he worked for, Woodruff & Sons, of Bradenton, had been hired by the Southwest Florida Water Management District to build the berm. The roller is designed to pack the sand, said Sgt. Elizabeth Brady of the Pinellas County Sheriff's Office.Winchester was pinned under the machine after it slipped and rolled on top of him. Co-workers saw the accident and used other pieces of equipment to free him.Winchester was pronounced dead at the scene. An investigation was under way Thursday night.