CHAMBERLAIN, S.D. - Before being sentenced to spend 30 years in prison for a 24-hour standoff, the man responsible for shooting a South Dakota highway patrolman asked the officer for forgiveness.

"There's not an hour of the day that goes by that I haven't thought about you or what I did," Donald London said to former state Highway Patrol Sgt. John Koenig on Tuesday. "I hope you can find it in your heart to forgive me someday."

London, 44, of Kimball, was sentenced Tuesday to a total of 75 years in prison on three counts of aggravated assault against a law enforcement officer, but 45 years of the sentence were suspended.

On Feb. 1, London pleaded guilty but mentally ill to the charges, which stem from an incident that began in frigid winter conditions on Jan. 7, 2015, in which he shot and injured Koenig, now a former Highway Patrol trooper.

"He chose to have a duel with Highway Patrol out there with a semi-automatic rifle. That was his choice," Koenig said during the sentencing hearing in Chamberlain.

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South Dakota Attorney General Marty Jackley previously called the standoff "one of the most dangerous events in South Dakota history."

Koenig thanked the medical and ambulance staff who treated him. He said his body temperature dropped to 92 degrees, and he had only 30 minutes left to live without treatment. Koenig said the medical staff saved his life, but they also saved London, who otherwise would have been charged with murder.

Law enforcement officers from across the state responded to the incident, including Mitchell police officers who brought an armored vehicle that protected eight officers inside. In total, 132 officers, dispatchers and other officials assisted during the standoff, which lasted from 3:45 p.m. on Jan. 7 until 3:15 p.m. the next day.

London, a former police officer from Wheatland, Wyoming, was diagnosed with numerous mental illnesses after the suicide of his wife, Ruth, on March 26, 2012. The diagnoses included depression, anxiety, substance-abuse disorders and psychosis, according to court documents.

His conditions came to a head in the days leading up to the standoff, in which London allegedly got in a bar fight in Kimball and threatened Chamberlain police officers with a rifle.

The defense called upon University of Cincinnati forensic psychologist Scott Bresler, who said placing London on probation would give him access to numerous treatment options in the community. Bresler said London has been taking medication for psychosis and an alcohol-use disorder and is no longer symptomatic.

"Mr. London is certain very intelligent and emotionally very capable of working and supporting himself while he's in the community," Bresler said.

Any treatment program would last at least 10 years, Bresler said.

On Jan. 6, London was taken to Dakota Counseling Institute in Mitchell, where he was diagnosed with severe depression, his medication was changed and then sent home. The shooting began about 12 hours later.

Bresler suggested London should have been hospitalized before the incident ever took place, and in another state, he may have been declared insane.

During sentencing, Judge Bruce Anderson discussed London's history of alcohol and substance abuse and his various mental illnesses, which could have kept London from recognizing Koenig, a man he was familiar with before the shooting.

"It may be very well the case that person he knew was standing in front of him telling him to drop a gun and he simply did not recognize him due to the psychotic episodes he was experiencing," Anderson said.

Anderson said Koenig still suffers physically from the shooting, and Trooper Adam Woxland, who was also on the scene, shows signs of post-traumatic stress disorder.

According to state law, London may serve part or all of his sentence in a treatment facility run by the Department of Social Services away from prison.

London's attorney, Tim Whalen, declined to comment after the hearing, but Brule County State's Attorney Dave Natvig said he expects London to serve his time in prison.

According to South Dakota law, London must serve at least 65 percent of the sentence, but he will be eligible for parole when he is 63 years old. He was also ordered to pay restitution of $375,770.67, which includes more than $200,000 to Brule County and $1,600 to Koenig.

Following the sentencing, Jackley issued a statement:

"This dangerous standoff demonstrates the very difficult work law enforcement officers face each day. I want to recognize the extraordinary effort of Sergeant John Koenig and all of our officers' heroism in overcoming the challenging standoff conditions. On behalf of law enforcement, we thank the outpouring of community support provided during this standoff," Jackley said.