Firefighter John H. Walsh, who witnesses say walked naked into a Rhode Island convenience store to buy a soda, will retire next month after four decades on the force. In a terse two-sentence statement, the town’s attorney said “Lynnfield has completed its investigation concerning Captain Walsh. He will come off administrative leave and retire in July.” The trouble began in April when a clerk at a 7-Eleven in Middleton, R.I., dialed 911 to report a nude man approached the register with his genitals exposed, smiled and bought a Coca Cola. Within minutes of leaving the store, his black Mercedes Benz was pulled over by police. When asked by the officer why he was being stopped, Walsh said, “it was probably because I went into the store to buy a Coke naked,” according to the police report.