(BAY COUNTY)   It was 40 years ago today that a 13 year old Bay City teen went missing near her home.  And while her body was since recovered, the reasons for her death and a suspect in the killing have eluded authorities.  Jan Marie Roher disappeared somewhere between her home and her school some three blocks away.  When the 8th grader didn't return home from school, her mother contacted authorities.  It wouldn't be for another year, that the girl's body would be found in a ditch in Zilwaukee Township.  She died of a gunshout wound to the head.  Officials say they ran through the list of suspects in the death, but were never able to get enough evidence to file charges.  Jan's family has never given up hope of solving the case.  Her brothers believe someone knows something and are pleading once again on the anniversary of her disappearance for them to come forward.  Anyone with information is being asked to call the Bay City Public Safety Department or CrimeStoppers at 1-800-422-5245