ST. PAUL — The boyfriend of a slain Minnesota teenager has pleaded guilty in her stabbing death.

Seventeen-year-old Anthony Mitchell of Maplewood pleaded as an adult Friday after waiving his adult certification hearing.

Mitchell will be sentenced to nearly 22 years in prison as part of a plea agreement.

Ramsey County Judge Gail Chang Bohr said juvenile certification would have resulted in too light a sentence.

Mitchell was charged with second-degree murder March 5, a week and a half after his 16-year-old girlfriend, Anna Hurd of North St. Paul, was found stabbed to death in a Maplewood park.

A witness told police that Hurd was trying to break up with her boyfriend.

Mitchell will be sentenced June 25.