Police said Lammers bought one firearm Monday and another Tuesday. He then went to the Missouri town of Aldrich to practice shooting because he "had never shot a gun before and wanted to make sure he knew how they shot and how they functioned," the probable cause statement said.
Hamilton said it appeared that Lammers obtained the firearms legally but that police were continuing to investigate "to determine how in fact he was able to obtain a permit."
Ashley Miller, who lives in a nearby town, said she has known Lammers for about a year and described him as "one of the sweetest guys I had ever met" but "very emotional," noting he would periodically stop talking to her.
She said he told her that he had bounced between relatives growing up. As an adult, he bounced between girlfriends, she said.
"He was never actually happy," she told the AP in a phone interview. "I think he had depression or something."
Polk County prosecutor Ken Ashlock said Lammers' first court appearance likely will happen Wednesday. He said his office would file a motion asking for a mental exam of Lammers. He said he wasn't aware of any charges in the 2009 Walmart incident.
Like the police chief, the prosecutor credited Lammers' mother for contacting police.
"It was a good thing they found what they found and took care of it," Ashlock said. "Everything was there as far as the weapons. He did have the weapons; he did have the ammunition ... Those things were all there, and then he made the statements to the officer about what his plans were."