CEDAR RAPIDS, Iowa (AP) — A man who was granted a new trial in the stabbing death of his ex-girlfriend has pleaded guilty to first-degree murder.

Television station KGAN reports that Luerkens was in court Thursday for a hearing on a motion, but unexpectedly changed his plea. He faces a mandatory life term when he's sentenced June 5.

Luerkens admitted stabbing 29-year-old Lynnsey Donald to death on April 21, 2015, in front of Donald's son in the Marion grocery store parking lot. He then injured himself.

The Iowa Court of Appeals last year ordered a new trial for Luerkens after ruling the trial court erred in denying his request to submit an insanity defense instruction to the jury.

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Information from: KGAN-TV, http://cbs2iowa.com