A St. Joseph teen will serve two consecutive life sentences for killing his grandparents.

Joseph Johnson was sentenced Wednesday in connection with the death of his grandparents 72-year-old James Johnson and 76-year-old Beverly Johnson in July of 2015.  Johnson was 16-year-old at the time of their deaths.

Johnson pleaded guilty in December to two counts of second-degree murder.

Buchanan County prosecutor Dwight Scroggins said Johnson will have to serve a minimum of 85-percent of his sentence before he is eligible for parole which means he would have to serve at least 51 years before he becomes eligible.