Police and U.S. Postal Service officials are investigating a complaint by a Meadowbrook area couple that a mail carrier fatally injured their Yorkshire terrier by hitting him with a rock. The 5-year-old dog named Maxwell wandered across the street from his owners’ residence in the 3600 block of Hazeline Road about 11 a.m. Saturday, Maxwell’s owner, Lawrence Brown, said Monday. Brown, 46, said he was in the garage and didn’t realize Maxwell was across the street when he heard a dog yelping in pain.