Loughner arrived and got in line with others waiting to meet the congresswoman. He opened fire about 10 minutes later as screams of "gun" rang out through crowd. Within moments, Giffords lay bleeding on the sidewalk with 11 others who were wounded. Six people were killed.
Almost everyone who crossed paths with Loughner in the year before the shootings described a man who was becoming unhinged.
He got fired from a clothing store and thrown out of college, shaved his head and got tattoos of bullets on his shoulder. He showed up at the apartment of a boyhood friend with a Glock 9 mm pistol, saying he needed it for "home protection." He made dark comments about the government, and, according to one acquaintance, appeared suicidal.
His spiral into madness hit bottom on that Jan. 8 day in 2011.
The information about Loughner's mental state — and the fact that no one did much to get him help — emerged as a key theme in roughly 2,700 pages of investigative papers released Wednesday. Still, there was nothing to indicate exactly why he targeted Giffords.
The files also provided the first glimpse into Loughner's family and a look at parents dealing with a son who had grown nearly impossible to communicate with.
"I tried to talk to him. But you can't," his father, Randy Loughner, told police. "Lost, lost and just didn't want to communicate with me no more."
His mother, Amy Loughner, recalled hearing her son alone in his room "having conversations" as if someone else were there.
Despite recommendations from Pima Community College that Loughner undergo a mental evaluation after the school expelled him, his parents never followed up.
In a statement released by the gun control advocacy group she started with her husband, Giffords said that "no one piece of legislation" would have prevented the Tucson shooting.
"However, I hope that commonsense policies like universal background checks become part of our history, just like the Tucson shootings are — our communities will be safer because of it."
While such checks may keep those with mental illnesses from obtaining guns, the 24-year-old Loughner had never been diagnosed with any conditions, meaning it's doubtful much would have stopped him from legally purchasing a weapon.
Friends and family interviewed by law enforcement after the shooting painted a picture of a young man who was deeply troubled in the weeks before the shooting.
Loughner visited Anthony George Kuck, who had known him since preschool. Kuck said he was alarmed to find he had shaved his head and was armed.
"I kicked him out of my house because he showed me his gun," Kuck said.
Kuck told police he had seen Loughner's mental state deteriorate over time, starting with drinking problems in high school, trouble with authorities and being kicked out of college.
"I know he has some crazy thoughts where he ... just believes the government is corrupt, and he has all these assumptions on things, that he doesn't really know what he's talking about," Kuck told investigators.
While he never heard him mention Giffords "he just seemed to have some kind of ... hate for government," Kuck added.
Kuck's roommate, Derek Andrew Heintz, who has known Loughner since he was about 12, said he was cooking when Loughner showed up with a gun and removed it from his belt. It was loaded with 32 rounds.
He asked Loughner why he had the weapon.
"I just want to show you,'" Loughner replied.
Loughner then left Heintz with a souvenir — one bullet.
His parents grew alarmed over his behavior on several occasions — at one point submitting him to drug-testing. The results were negative, said Amy Loughner, who was particularly worried that her son might have been using methamphetamine.
The father said his son kept journals, but they were written in an indecipherable script. Loughner bought a 12-gauge shotgun in 2008, but his parents took it away from him after he was expelled from college and administrators recommended he not own weapons.
On the day of the shooting, he and his father got in an argument, and he chased Jared Loughner away from their house. Friend Bryce Tierney told investigators Loughner called him early in the morning that day and left a cryptic voice mail that he believed was suicidal.
"He just said, 'Hey, this is Jared. Um, we had some good times together. Uh, see you later.' And that's it," Tierney said.
Onetime Loughner friend Zachary Osler explained how he worked at a sporting goods store where Loughner bought the handgun used in the shooting. He was questioned about seeing Loughner shopping there sometime before Thanksgiving and described an awkward encounter with the man.
"His response is nothing. Just a mute facial expression. And just like he, he didn't care," Osler told authorities.
News organizations seeking the records were denied access in the months after the shooting and the arrest of Loughner, who was sentenced in November to seven consecutive life sentences, plus 140 years, after he pleaded guilty to 19 federal charges.
Last month, a judge cleared the way for the release of the records after Star Publishing Company, which publishes the Arizona Daily Star in Tucson, joined by Phoenix Newspapers Inc., which publishes The Arizona Republic, and KPNX-TV, sought their release. The judge said Loughner's fair-trial rights were no longer on the line now that his criminal case has resolved.
Loughner's guilty plea enabled him to avoid the death penalty. He is serving his sentence at a federal prison medical facility in Springfield, Mo., where he was diagnosed with schizophrenia and forcibly given psychotropic drug treatments to make him fit for trial.
Loughner's attorney, Judy Clarke, didn't return a call seeking comment Wednesday. There was no listed telephone phone number for Randy and Amy Loughner.
Arizona's chief federal judge and a 9-year-old girl were among those killed in the rampage. Giffords was left partially blind, with a paralyzed right arm and brain injury. She resigned from Congress last year.
Giffords intern Daniel Hernandez described how constituents and others were lining up to see Giffords on the morning of the shooting. He helped people sign in and recalled handing the sheet on a clipboard to Loughner.
"The next thing I hear is someone yell, 'Gun,'" said Hernandez, who rushed to tend to Giffords' gunshot wound to the head.
"She couldn't open her eyes. I tried to get any responses from her. It looked like her left side was the only side that was still mobile," Hernandez told authorities. "She couldn't speak. It was mumbled. She was squeezing my hand."
Hernandez explained how he had some training as a nurse and first checked for a pulse.
"She was still breathing. Her breathing was getting shallower," he said. "I then lifted her up so that she wasn't flat on the ground."
When he was arrested at the scene, Loughner was wearing peach-colored foam earplugs and had two loaded magazines in his left front pocket for the Glock he used in the shootings.
Hours later, he was polite and cooperative as detectives began their initial interview.
As Loughner sat in restraints in an interview room, the conversation was confined mainly to small talk. Little was said over the first four hours. Loughner asked if he could use the restroom, then at one point complained he felt sore.
"I'm about ready to fall over," he said.
Today, Giffords is still recovering. She struggles to speak in complete sentences and often walks with the help of her husband.
In a January interview on ABC News, she said "daggers" to recount her tense, face-to-face encounter with Loughner at his sentencing. When asked to describe his mental illness, she said one word: "sad."
Associated Press writers Michael R. Blood and Justin Pritchard in Los Angeles contributed to this report.