The Minneapolis church shooter who killed two children and wounded 21 others during a Catholic school Mass bought a firearm four days beforehand, according to a local gun shop owner.

Robin Westman opened fire on a school-wide Mass at Annunciation Catholic Church on Aug. 27 at around 8:30 a.m., shooting from outside the building through the stained-glass windows.

Westman, 23, died by suicide from a self-inflicted gunshot. Westman, who was born Robert Paul Westman and underwent a legal name change in 2019, according to court documents, attended the school and its associated church, located next door.

Kory Krause, owner of Frontiersman Sports in St. Louis Park, Minnesota, provided security video of Westman entering his store and buying a small pre-owned .38 Special revolver four days before the shooting, which was purchased legally. That gun wasn’t used in the shooting at Annunciation Catholic Church, he said.

Westman can be seen holding a firearm at Frontiersman Sports. (Kory Krause)

“There were absolutely no red flags displayed by the individual in question. They acted perfectly normal,” Krause said. “They fit right in with other shoppers. They said the right things, asked the right questions, appeared completely genuine, friendly, personable, and dare we say ‘normal.’ All of us here at Frontiersman are absolutely heartbroken about this tragedy. We ask ourselves constantly if there was anything we missed, anything we could have done better, and sadly the answer is no.”

When staff at the store entered Westman’s information into the FBI’s National Instant Criminal Background Check System, it flashed a “proceed” signal, and the firearm was purchased lawfully, Krause said.

Robin Westman was seen browsing Frontiersman Sports. (Kory Krause)

“My staff has a stellar reputation with local and federal law enforcement for being the best in the business at weeding out bad actors. All my staff has many years’ experience in detecting and preventing attempted straw purchases, sales to those who appear mentally unstable in any way, suicidal, homicidal, intoxicated or under the influence of drugs, and those we deem incompetent, unsafe or unfit to possess a firearm for various other reasons,” Krause said. 

“We decided to come forward with the information we have regarding the shooter in the hope that it would add some more perspective to the horrible situation that occurred,” he added.

Fox News Digital reached out to the Minneapolis Police Department for comment.

Fox News’ Peter D’Abrosca contributed to this report.