MINNEAPOLIS — A man accused of killing a prominent Minnesota doctor before he was shot by police in the doctor’s front yard appears to have been angry over the way the physician handled his mother’s medical treatment, authorities said Monday.

Few other details were released about what led up to the slaying of Dr. Stephen Larson, an obstetrician and gynecologist who was shot multiple times after he answered a knock at the door of his home in the Minneapolis suburb of Orono. Authorities said Larson was home alone Friday night and talking on the phone when he heard the knocking.

“The doctor said he was going to answer the door. He did. The person on the other end of the line … heard some words, some noises. The doctor never came back to the open phone line,” Hennepin County Sheriff Rich Stanek said. The person hung up and called 911. Orono police arrived to find Ted Hoffstrom, 30, in Larson’s front yard, wielding a semi-automatic handgun.

“After diligent attempts to negotiate with Mr. Hoffstrom, shots were fired,” Stanek said. “Mr. Hoffstrom died at the scene.”

Authorities went into the house and found Larson dead from multiple gunshot wounds. Stanek said Hoffstrom is the only suspect in Larson’s death, and the gun Hoffstrom had with him was the murder weapon.

“We know who committed this murder, yet many unanswered questions remain,” Stanek said.

Stanek said that during their preliminary investigation, authorities learned Larson had provided medical care to Hoffstrom’s mother at one time, and that Hoffstrom had recently expressed hostility about the doctor. He did not elaborate on the nature of the hostility, citing medical privacy rules as well as the ongoing investigation into the officer-involved shooting of Hoffstrom.

Orono Deputy Police Chief Chris Fischer said the four officers involved in Hoffstrom’s death, including the police chief, are on paid administrative leave pending the investigation, per department policy.

Larson had been practicing medicine since 1970 and has delivered thousands of babies in his career. He started his own clinic, Obgyn Specialists, which has clinics in Edina and Burnsville, in 1980. He was active in the medical community, and had been working as an adjunct professor at the University of Minnesota Medical School since 2004.

Sandy Kamin, clinic administrator, said she worked with Larson for 25 years and his death came as a “complete shock.”

Kamin said Larson had a marvelous sense of humor and treated his colleagues like family — greeting each one of them as his “favorite.” He established his clinic, Kamin said, because focusing on quality patient care was important to him. In addition to medical care and delivery of babies, Larson was also a surgeon, and spoke internationally on the topic of vaginal surgery.

“He really set the bar high, and we all tried to reach it — and he let us know if we did, and let us know if we didn’t,” Kamin said. “He really wanted to have the best clinic in town for women.”

Hoffstrom, an attorney, graduated from the University of St. Thomas School of Law in 2009.

Katharine Tinucci, campaign manager for Gov. Mark Dayton, went to law school with Hoffstrom and was stunned to hear of his involvement. She last saw him about a month ago when the two crossed paths in the parking lot of the state Democratic Party, where Hoffstrom was working part-time on a phone bank.

“Ted was genuinely compassionate and very kind to his classmates,” she said. “You would never suspect any kind of trouble in his life.”

Messages left at the homes of Larson and Hoffstrom were not immediately returned.