(CNN) -- Jared Loughner's behavior was so disturbing that his father confiscated his shotgun and took to disabling his car every night to keep him home in the months leading up to an Arizona shooting rampage that left six people dead, according to investigative documents released Wednesday.
Loughner's parents even went so far in the days and weeks before to tell their son he needed to get help "(be)cause his behavior is, um, been not normal," his mother, Amy, told investigators, according to transcripts of recorded interviews by investigators.
The documents reveal vivid details about the events leading up to and surrounding the January 8, 2011, shooting during a meet-and-greet with U.S. Rep. Gabrielle Giffords outside a Tucson, Arizona, grocery story. Giffords, who was shot in the head, was among 13 people wounded in the shooting.
The statements by Loughner's parents were among the more than 2,700 pages of previously sealed documents released by the Pima County Sheriff's Department in response to a Freedom of Information requests filed by CNN and other news agencies.
Loughner, 24, is serving a life sentence without the possibility of parole after pleading guilty last year to 19 charges in exchange for the government not seeking the death penalty.
Many of the details surrounding the rampage are well known, from the heroic efforts to save Giffords and others to the tackling of the gunman.
But the documents shed light on Loughner's erratic behavior leading up the shooting, from fleeing from his father the morning of the shooting to his repeated effort to buy ammunition for a 9mm handgun that he ultimately used in the rampage.
Loughner's parents told authorities that their son, who they described as a "loner," took a turn following his dismissal from Pima County College months earlier -- after he posted a disturbing video online that officials described as threatening.
Loughner's parents told authorities they took away his shotgun after college police warned them their son may be a danger to himself or to others.
Efforts for ammo, tears at traffic stop
Her son never followed up on getting a mental health evaluation that was required for being readmitted to the college, Amy Loughner said.
According to the documents, unbeknownst to his parents Loughner purchased a 9mm handgun sometime before Christmas 2010 and showed it off to a friend.
On the morning of the rampage, he went to at least two Walmarts in an attempt to buy ammunition. He was turned away at one by an employee who told investigators that he was behaving strangely.
"I kind o' felt uneasy, to be honest with you," the employee was quoted as saying in the transcripts.
At another Walmart, Loughner was described as friendly as he inquired whether there was a limit on the amount of ammunition he could purchase.
"And then I guess he asked for six boxes, seven boxes," an employee said. "Rang them up. Checked his ID. Wasn't any problem. So I double-bagged it for him.'
Just hours before the rampage, Loughner broke down and cried to an Arizona Game and Fish officer when he pulled over for running a red light.
"It's bad for your health, you're gonna kill somebody, you're gonna kill yourself," Game and Fish Officer Alen Edward Forney told Loughner, according to the transcript of Forney's statements to investigators.
"I said, 'I'm not gonna write you a citation for this.' And when I said that to him, his face got kinda screwed up and, and he started to cry.
"That struck me as a little odd," Forney continued. "So I asked him if he was OK. And he said, 'Yeah, I'm OK, I've just had a rough time and I really thought I was gonna get a ticket and I'm really glad that you're not.' "
But Forney was worried whether Loughner could drive safely.
"I again made sure that he was OK. I asked him ... three or four times. He was probably getting tired of me asking if he was OK," Forney said.
"He said yeah, he was fine. He was just heading home, it wasn't too far away and he'd be OK," Forney said.
Two and a half hours later, Loughner opened fire on a crowd of people at an outdoor event where Giffords was greeting constituents.
When Forney got home that night and heard about the shooting, he went online, he said.
"I opened up the Internet and there was his picture," Forney said. "Man, my heart just went up in my throat."
About an hour after the traffic stop, Loughner returned to his parents' home in his 1969 Chevrolet Nova, his mother, Amy Loughner, told authorities.
When his parents asked him what was in his backpack, he ran out the door, his mother said.
His father, Randy Loughner, dropped his coffee and ran after his son but couldn't catch him, the mother said.
A short time later, a neighbor told them there were news reports Giffords had been shot.
They later learned from authorities their son was believed to be the shooter.
Kenneth Veeder, a bystander to the shooting, suffered a gunshot wound to the calf as he was talking to a family lined up to meet Giffords. Veeder, a Vietnam War combat officer who served three tours of duty, was wearing an Infinity Airborne shirt.
"I heard pop, pop, pop, pop," Veeder said.
Loughner was running and knocked him down, he said.
When Loughner was reloading his gun, one man grabbed him, and Veeder grabbed Loughner's gun that fell to the ground, Veeder said.
Veeder wanted to reload the gun, but a woman talked him out of it.
"She goes, 'You can't do that,' " Veeder said in the transcript. "The hell I can't -- because I would have shot him. That's how angry I was. It was a combat reaction," he said.
Deputy Sheriff Thomas Audetat Jr. recounted how he arrested Loughner. He saw two or three people holding down Loughner on a sidewalk between a Safeway grocery and Walgreens.
Audetat put his knee on Loughner's back and handcuffed him.
A bullet had earlier grazed the left side of the head of one person holding down Loughner, Audetat said. Right behind him was a woman who was also a gunshot victim.
Audetat searched Loughner.
"In his left front pocket, I found two magazines which I immediately observed to be for a Glock," Audetat said. "I was not sure of the caliber at that point, but they were Glock magazines and they were both fully loaded."
Audetat also found a foldable knife with a 4-inch blade in Loughner's front pocket.
Loughner said he was feeling hot, so the deputy removed Loughner's beanie and hooded sweatshirt.
Audetat found Loughner wearing earplugs, and Loughner also stated several times that he pleaded the Fifth Amendment, documents said.
"At that point, he said, 'I just want you to know that I'm the only person that knew about this,'" Audetat said. "That was the only thing, pretty much, that he said to me almost all day."
CNN's Deanna Hackney, Stan Wilson, Dugald McConnell, Shawn Nottingham, Emily Blakemore and Brian Todd contributed to this report.