BUFFALO, N.Y. (AP) — An 18-year-old girl has been sentenced to 20 years to life in prison for her part in the beating and stabbing death of her step-grandfather in his western New York home.

Erie County District Attorney John Flynn calls Thomas Heath's murder "by a young girl who he loved" one of the most disturbing cases his office has seen.

Alexandria Heath of Buffalo was sentenced Thursday to the same prison term her 20-year-old boyfriend, Romaine Jirdon, received in December.

Prosecutors say the couple intentionally killed 58-year-old Thomas Heath in November 2017. They have not revealed a possible motive.