The police were investigating yesterday whether the young off-duty transit officer who reported finding a burning backpack in the Times Square subway station on Monday night might have actually planted it there himself and detonated the pipe bomb inside, several police officials said. The explosion panicked riders and shut down part of the busy station shortly after the evening rush. On Monday night, the police had at first credited the officer with discovering the device, warning commuters away, and burning himself as he called for backup. The officer has not been charged with any crime, and the police officials said...