BUFFALO — An alleged gunman’s addiction to opioid medication was the “driving force” behind last week’s shooting at a Minnesota health clinic that left one person dead and four injured, a veteran investigator said in his application for a search warrant.

Wright County Deputy Patrick Bailey said authorities found a plastic bag containing six oxycodone pills when they searched Gregory Ulrich’s hotel room after the Feb. 9 shooting at an Allina Health clinic in Buffalo, a small city about 40 miles (65 kilometers) northwest of Minneapolis. Bailey also described a video in which Ulrich mentioned taking more than 30 pills at a time.

“It is clear to your affiant that Ulrich has a dependency on opioid style pain medications, and was upset that his legal supply had been stopped,” Bailey wrote in the warrant application, which was obtained by KARE-TV. “Your affiant also believes that Ulrich’s dependency on pain medication is the driving force behind his assault which resulted in the death of Lindsay Overbay and multiple serious injuries to others.”

Ulrich, 67, is charged with murder, attempted murder and other counts in the shooting that left Overby, a 37-year-old medical assistant, dead. According to the charges, Ulrich walked into the clinic and began shooting staff after they asked if they could help him. He shot two people in the reception area and three others in the clinic’s interior. He is also accused of setting off three suspected pipe bombs.

Bailey wrote about Ulrich’s apparent dependency on opioids in an application for a search warrant for Ulrich’s medical records.

KARE-TV reports that Ulrich had back surgery in 2016, and shortly after that, he was taken back to the hospital after overdosing on opioids, which led a doctor at the clinic to cut off his supply of pain medication.

Court documents show that Ulrich threatened a mass shooting at the clinic in 2018. That threat led to a restraining order that barred Ulrich from the clinic and a nearby hospital and ordered him to have no contact with a doctor. Ulrich tried to plead guilty in May 2019 to violating the restraining order, but a judge didn’t accept his plea. A charge of violating the restraining order was dismissed last April when the prosecutor said Ulrich was found “mentally incompetent to proceed.”

“Through training and experience, Your Affiant knows individuals who abuse controlled substances, such as Oxycodone, are often unable to obtain through legal means. Your Affiant also knows that people who obtain Oxycodone legally, rarely store the pills in a sandwich bag,” Bailey wrote.