A motorcyclist is dead and the driver of an 18-wheeler is sought after a deadly hit and run in St. Martin Parish, according to Louisiana State Police. Troopers identified the motorcyclist as Harvey Gauthier, 49, of St. Martinville. They said the incident happened on LA 347 near Lou Gauthier Road, which is south of St. Martinville, on Friday, October 17, a little after 5 a.m. They added Gauthier was riding a 2007 Honda off-road motorcycle when it suddenly braked, he lost control, and he fell off on the highway. They noted the reason for the abrupt braking is still under investigation. According to troopers, an 18-wheeler rolled over Gauthier while he was still lying in the roadway and left the scene…