A central Minnesota teenager pleaded guilty Friday to killing a 20-year-old Twin Cities college student with a single punch in a St. Cloud alley.

Jesse J. Smithers, 18, of Sauk Rapids, entered his plea to second-degree unintentional murder in Stearns County District Court in the death of Colton R. Gleason, of Greenfield, on Sept. 20.

A jury trial for Smithers was scheduled to start Tuesday. Sentencing is scheduled for Feb. 6, and both sides agreed to a term of 10 years, said Assistant County Attorney Will Brost. State guidelines called for 10 years and eight months.

Authorities have not revealed what prompted the late-night confrontation on Sept. 20, 2012, three blocks east of St. Cloud Tech, where Smithers was a high school senior. Police and family members said it did not appear that Gleason knew Smithers.

“There isn’t a rational explanation” for what Smithers did, Brost said, adding that he at first made a claim of self-defense.

The prosecutor said it’s possible that a motive could surface during sentencing.

Smithers was driving west of St. Cloud State University through an alley in the 600 block of 8th Avenue S., where Gleason and two women were walking about 11:20 p.m.

Smithers got out and punched Gleason in the head, causing him to hit his head on the ground. He died the next day at St. Cloud Hospital.

Gleason’s family said he was a sophomore at Minnesota State University, Mankato, and was visiting friends in St. Cloud.