-- Police shot and killed a corrections officer last night. Marquis Barker, 38, an officer at Nashua Street Jail, was gunned down after stealing a police cruiser and leading officers on a chase through Dorchester and Mattapan. Police responding to calls found Barker out of control outside his Dorchester home, wielding what appeared to be a handgun. Barker begged police to shoot and kill him before escaping in the police cruiser. After crashing the cruiser......