Originally Published: 03 JUN 22 13:07 ET

By Rebekah Riess, CNN

(CNN) -- Gregory Ulrich, who killed one person and wounded four others in a mass shooting last year at a Minnesota health center, was found guilty Thursday of first-degree premeditated intentional murder, first-degree premeditated attempted murder and other charges, according to Wright County Attorney Brian Lutes.

Ulrich, who opened fire and detonated improvised explosive devices on February 9, 2021, at the Allina Heath Care Clinic in the city of Buffalo, was convicted of all 11 counts against him following a three-week trial, the prosecutor said.

First-degree premeditated murder carries a mandatory life in prison without the possibility of parole sentence, according to Lutes. Ulrich will be sentenced June 17.

"That was the only acceptable sentence, in the state's view, for the horrific crime that he committed," Lutes said. "The verdict that this fine jury handed down holds Gregory Ulrich accountable for the horrific crime that he committed."

CNN has reached out to Ulrich's attorney, Gregory Davis, for comment.

On the day of the attack in Buffalo, about 40 miles northwest of Minneapolis, Ulrich "pulled out a handgun and began threatening clinic staff" when they asked if they could help him, according to a criminal complaint.

Ulrich then opened fire in the reception area, the complaint said, striking one person in the back with a round of 9 mm ammunition. A second victim was shot in the abdomen.

In the clinic's interior, the complaint said, Ulrich shot a third victim twice in the back of the upper leg as the victim tried to escape. A fourth victim was struck with six rounds -- one in the left chest, one in the abdomen, one in the back, one to the upper left arm and two to the left forearm.

A fifth person was shot in the abdomen, and the bullet passed through the victim's liver and spine before exiting through the victim's back, according to the complaint.

Ulrich, after the assault, called 911 to tell authorities he would surrender, according to prosecutors.

The gunman had detonated two improvised explosive devices, the complaint said, while a third remained unexploded.

All five victims were Allina Health employees, the company said.

Lindsay Overbay, a medical assistant at the facility who had worked for the company since 2018, was killed.

After the assault, Buffalo Police Chief Pat Budke told reporters Ulrich was "very familiar" to law enforcement and was upset with his treatment at the clinic.

Ulrich, who was taken into custody after the shooting, likely targeted the facility because of "a history of him being unhappy with health care -- with the health care he received," the chief said at the time.

Richard Ulrich told CNN last year that his brother often complained about "pain medication he needed and how they wouldn't give it to him."

"He just seemed obsessed with that," Richard Ulrich said.

In 2018, Gregory Ulrich called the health center and threatened shooting and "blowing things up" in "revenge" for his anger at the medical community, said a doctor who reported the threat, according to a Buffalo police report obtained by CNN last year.