Kill Me Why

From the horrible nation case in 1989, when Tassanee disappeared from home without reason. The best police officer was assigned to investigate the kidnap case, a daughter of the food shop owner. But the more he investigated, the more he got some clues. The suspect became the best teacher of the province and beloved by everyone. Before police found the dead end, young girl's body was found. As if she woke up to ask for justice. She was murder cruelly by cover after kill with concrete and weight into the water. Was he a real killer? If so, what made him do that?