(CBS News)--BOLIVAR, Mo. - On Friday, a young man who told Missouri police he intended to commit mass murder was convicted of planning an armed assault.
The case of 21-year-old Blaec Lammers is the story of how difficult it is for many parents to get adequate medical care for their mentally-ill children.
Lammers has been in custody for the last 15 months in Bolivar, Mo., for plotting mass murder."I watched a scary movie one day and that thought came back in my mind," he said. "I could do this."
Could do what?
"Hurt somebody," he said.
Was he actually thinking he could kill somebody?
"At times I did," he said.
"I just walk in and start shooting, and just wait till the police got there," he said in the confession.
"Police got here and do what?" an officer asked him.
"Just hand myself over," he answered.
Tricia Lammers had discovered a receipt in her son's pants.
"I found a receipt that said 'Shotgun, $865," she said.
It turns out that shotgun receipt was actually for an assault weapon. She called police.
Lammer's father, Bill Lammers, was asked whether she had done the right thing.
"Yeah, and I'll tell you why," he said. "Our son is still alive today and no one else was hurt."
Blaec's parents first noticed changes in their son's mental state when he was 16. Seven times in the next four years he would be admitted to psychiatric hospitals following escalating threats of violence.
Each time he was released after four days -- the legal limit without a hard-to-obtain court order -- with new medications and a new diagnosis, ranging from a form of autism to bi-polar to a condition linked to schizophrenia.
Does Blaec Lammers consider himself mentally ill?
"If I stay busy, I'm good," he said. "But if I get bored, or I'm by myself, I get to thinking of stuff."
And that stuff could be suicidal or homicidal, he said.
But he was never involuntarily committed during his seven trips to mental hospitals, so nothing came up on his background check and he was able to go into Walmart and buy two AR-15 style rifles, similar to the gun used in the Aurora, Colo., movie theater shooting and in Newtown, Conn.
Was he capable of shooting up a movie theater?
"It was a 50/50," he said.
Lammers could get life in prison when he is sentenced in March.
The defense could have asked for him to be put in a mental-health facility.
But before the verdict, the judge asked Lammers if he had any interest in that. He said no.
So his only option now is prison.