FORT PIERRE, S.D. — A jury has convicted a South Dakota man of fatally stabbing his ex-girlfriend nearly two dozen times.

Thirty-four-year-old John Hemminger, of Aberdeen, was found guilty Wednesday of first-degree murder in the January 2015 death of Jessica Goebel. The conviction carries a mandatory life sentence.

Jurors in Fort Pierre returned the verdict in roughly five hours after attorneys presented closing arguments.

Authorities accused Hemminger of stabbing Goebel 23 times when she refused to take him back after a breakup. The Aberdeen American News reports prosecutors presented evidence showing that the DNA of Hemminger and Goebel was found on the knife blade authorities believe was used in the stabbing.

Hemminger’s defense maintained someone else is responsible for the killing, and that police bungled the investigation.

It wasn’t immediately clear whether a sentencing hearing has been set and if Hemminger plans to appeal.