"[Loughner] advised that he drank the alcohol because he was very upset as his father yelled at him," according to the May 2006 Pima County Sheriff's office police report obtained by ABC News. "I could see his eyes were very red and he was crying...I was advised that he had stolen the alcohol from his father's liquor cabinet." He was charged with charged as a minor with possession of alcohol.
Loughner was also arrested when he was a teenager for marijuana possession.
And once enrolled at Pima Community College, Loughner was investigated five times by campus police.
In February 2010, police interviewed Loughner after a teacher referred to him as "creepy" and as having a "dark personality" after he allegedly suggested that a girl who had written a poem about an abortion strap a bomb to the baby.
The campus officer eventually determined that the incident did not "justify making contact with Loughner by police," according to the report.
A few months later, a teacher called campus police after Loughner grew "very hostile" upon learning that his grade in his pilates class was a "B." According to the report the teacher felt "intimidated" and had concern that Loughner might turn physical, requesting that an officer "be nearby" on the last day of class. Campus police monitored the classroom, but never spoke to Loughner about the complaint, the report says.
Over time, Loughner's behavior appeared to become stranger.
In September, after Loughner disrupted a math class, an officer who questioned the suspect about the incident wrote, "Loughner's head was constantly tilted to the left and his eyes were jittery."
The next week, when officers went to tell Loughner that he had been suspended from Pima after violating the student code of conduct for taping a YouTube video on campus during which he declared the college unconstitutional, the 22-year-old held a constant trance of staring at the school official.
The official wrote in a report that Loughner stared at him for an hour as the official spoke to the student and his father. When Loughner did finally speak, he said, "I realize now that this is all a scam."
The details of Loughner's behavior the morning of the shooting were also bizarre.
At 5 a.m. Loughner posted a message on his MySpace page, writing, "Goodbye friends...don't be mad at me."
Then his attempt to buy ammunition at a Wal-Mart was rejected because the salesman found his behavior to be "erratic," but Loughner was successful buying the clips at a different Wal-Mart.
At 7:30 a.m., Loughner ran a red light and was pulled over by an Arizona Game and Fish Department officer. The officer found no outstanding warrants and let Loughner go with a verbal warning to drive carefully.
Just a half hour later, Loughner's father Randy spotted him pulling a black bag from the trunk of their car. Loughner's father followed his son in his car, but lost him.
Less than two hours later Loughner took a taxi to Rep. Gabrielle Giffords event, and 13 minutes later, Loughner was allegedly firing.
ABC News' Eloise Harper contributed to this report.