A southwest Missouri man who confessed this week to plotting to shoot up a "Twilight" showing and a Walmart store was detained in 2009 after threatening a store clerk, police said Saturday.

Bolivar Police Chief Steve Hamilton said Saturday that Blaec Lammers, 20, of Bolivar, followed a female clerk around a Walmart store in 2009, threatening her. He wasn't charged, but was committed for 96 hours for a mental health examination. Lammers, whose own mother turned him in Thursday, faces three felony charges in the alleged shooting plot.

In Missouri, hospitals, law enforcement officials and private citizens can request a person be held against their will for up to 96 hours if he or she appears to be a threat to themselves or others.

"It looks like everything was done appropriately at that time," Hamilton said. "The average person will look at it and say `Why was he not charged criminally?' And the reality is the law only allows so much when a person is having some mental issues."

Lammers was charged Friday with first-degree assault, making a terroristic threat and armed criminal action. He is jailed in Polk County on $500,000 bond. Those charges focus on the alleged Walmart plot.

Polk County prosecutor Ken Ashlock said Friday that his office would file a motion asking for a mental exam of Lammers.

Phone messages left by The Associated Press at Lammers' home weren't returned Friday or Saturday. No attorney is listed for him in online court records.

The investigation into the shooting plot began Thursday, when Lammers' mother contacted authorities, saying she worried that her son "may have intentions of shooting people" during the opening weekend for the final film in the popular vampire series, police wrote in the probable cause statement.

She said her son recently had purchased weapons -- two assault rifles and hundreds of bullets -- that were similar to those used by a gunman who opened fire inside a theater in Aurora, Colo., during the latest Batman movie in July. That attack killed 12 people.

Police wrote in the probable cause statement that Lammers was "off of his medication."

Hamilton said Saturday he didn't have details about Lammers' mental condition, although he said Friday that Lammers was under a doctor's care.

Lammers was questioned Thursday afternoon and told authorities he bought tickets to a Sunday "Twilight" screening in Bolivar and planned to shoot people inside. The town of roughly 10,000 people is about 130 miles southeast of Kansas City.

According to the probable cause statement, Lammers also said he planned to "just start shooting people at random" at a Walmart store less than a mile away. He said he'd purchased two assault rifles and 400 rounds of ammunition, and if he ran out of bullets, he would "just break the glass where the ammunition is being stored and get some more and keep shooting until police arrived," investigators wrote.

Police said Lammers bought one firearm Monday and another Tuesday, then went to Aldrich to practice because he "had never shot a gun before and wanted to make sure he knew how they shot and how they functioned."

Hamilton said it appeared that Lammers obtained the firearms legally.

He said his office has no information to indicate anyone else was involved but was interviewing people just to be certain.

Hamilton said it's "very difficult to say what (Lammers) would have done."

"I think he would have been adaptive," Hamilton said. "If one target wasn't available, I think he would have changed to something else."