(AP) — An Omaha teenager convicted of killing his ex-girlfriend has been sentenced to several decades in prison.

Douglas County District Judge Russell Bowie gave Justin Lenz on Wednesday a 60- to 80-year sentence. He pleaded guilty last August to second-degree murder in the May 2012 death of 16-year-old Melanie Koontz.

Lenz must serve 30 years in prison before he is eligible for parole.

Koontz’ body was found in an Omaha creek. Investigators say she was strangled.