(ABC News) -- The Missouri man accused of planning a movie theater massacre at a screening of the final "Twilight" movie was arrested once before, in 2009 after stalking a Walmart clerk with a knife and rubber mask, according to a newly released arrest report.
Blaec Lammers told investigators in Oct. 2009, he went to the Walmart in Bolivar, Mo., looking for an "easy victim" after watching the horror film "Halloween," saying that watching the main character killing people "got him to thinking," the arrest report said.
Lammers, then 17, told authorities he watched the clerk for more than two hours. He said he was planning to follow the clerk into a storage room and kill him. Lammers' plan fell apart when his mother located a suicide note and noticed a kitchen knife was missing. She called the authorities, who located Lammers' car in the Walmart parking lot.
No charges were filed in that case. Instead, Lammers was committed for 96 hours for a mental health examination, Polk County prosecutor Ken Ashlock said Tuesday.
Blaec Lammers, now 20, was charged Friday with first-degree assault, making a terroristic threat and armed criminal action after his mother alerted police that he had purchased 400 rounds of ammunition and two assault rifles "very similar to the ones in Aurora, Colo., movie theater shooting," according to probable cause statement issued by the Bolivar Police Department.
Speaking for the first time since she turned her son into police, Tricia Lammers told reporters Tuesday at the National Alliance for Mental Illness in Springfield, Mo., that she is not a hero for her actions.
"First and foremost I am a mother and I love my son very, very much. Second, I am not a hero. I love my community just as much as I love my son. I respect the people who live in my community and I respect their safety and their right to be safe," Lammers said.
During the nearly 20-minute long press conference, Lammers said her son is a good kid with a good heart but suffers from anti-social personality disorder, depression and Asperger's Syndrome.
"I think any mom, at any time, would blame herself that she did something wrong," Lammers said with tears in her eyes.
Blaec Lammers confessed to police that he purchased two assault rifles and hundreds of rounds of ammo at an area Walmart last Monday and got his friend to teach him how to shoot the following day in Aldrich, Mo., according to probable cause statement.
Lammers told police he planned to commit a mass shooting at a midnight showing of "The Twilight Saga – Breaking Dawn Part 2" in Bolivar and even purchased a ticket.
Lammers said he also planned to shoot up a nearby Walmart – the same store from the 2009 incident -- according to the statement.
According to the police probable cause statement, Tricia Lammers became suspicious after finding receipts for his new assault rifles. Lammers was also worried that her son might be off his medication and contacted police. Lammers was in police custody within an hour after his mother got in touch with the authorities, according to Bolivar City Administrator Darin Chappell.
"For a guy to plan out something like that, it would take a lot of planning and I don't see Blaec doing something like that," said Ethan Mason, a friend of Lammers'.
Lammers made a brief court appearance Tuesday, where prosecutors determined he should undergo a mental health evaluation.
"Hopefully Blaec will get the help he needs. He is not a criminal," Tricia Lammers said.
His next court appearance is scheduled for Jan. 23.
ABC News' Mosheh Gains, Russell Goldman and The Associated Press contributed to this report.