ST. PAUL — A South St. Paul man was sentenced Tuesday to 40 years in prison for fatally shooting a Minnesota National Guardsman last year after being convinced by the victim’s wife that he was abusing her.

Aaron Allen, 26, pleaded guilty in March in Ramsey County to second-degree intentional murder in the killing of 25-year-old Staff Sgt. Brandon Horst of St. Paul early on Aug. 5 and agreed to the prison term. Allen testified at his plea hearing that he shot Horst because he believed that Horst had abused his wife, causing her to miscarry three times when she never was pregnant.

Allen reportedly apologized to Horst’s family in court Tuesday.

“I can’t turn back time, but I will use my time in prison to make myself a better person,” Allen said.

He had testified that he was abused as a child and witnessed his mother being abused as well.

He said that when Horst’s wife, Heather Horst, told him on Aug. 4 that her husband caused her to miscarry again, he saw “red.” He testified that he decided to kill Brandon Horst after the victim’s wife said she wanted him dead and promised Allen $100,000 to do it.

Allen testified that Heather Horst drove him to the couple’s house on St. Paul’s West Side and let him in. Allen told the court he waited in the basement for a few hours before creeping upstairs and shooting Brandon Horst once in the right eye.

Heather Horst, 25, was convicted in May for her role in the slaying and immediately sentenced to life in prison without parole.

At Allen’s sentencing, Judge John Guthmann said it didn’t matter if Allen might have been tricked because his actions directly led to Brandon Horst’s killing. He described Allen’s act as “cowardice.”

“He went overseas to serve his country,” the judge said. “He went overseas to serve you.”