Loughner, 22, has been described as a social outcast with wild beliefs steeped in mistrust. He faces charges that he tried to assassinate Rep. Gabrielle Giffords in an incident that left six people dead.
Special Section: Tragedy in Tucson
According to Pima, Loughner was a student from the summer of 2005 though the fall of 2010. From February to September 2010, Loughner had five "contacts" with campus police for classroom and library disruptions. On Sept. 29, campus police found that he had filmed a video on YouTube that claimed the college was illegal according to the U.S. Constitution.
The college administration immediately suspended Loughner and delivered a letter of suspension to Loughner's parents' home. According to the Pima, police officers spoke with both Loughner and his parents.
The letter barred Loughner from returning to campus expect to set up an appointment and discuss the school's code of conduct and his suspension.
On Oct.4, Loughner and his parents met with college administrators and withdrew from school. On Oct. 7, Pima sent a letter to Loughner telling him that if he intended to return to school, he would have to get a letter from a mental health official indicating "his presence at the College does not present a danger to himself or others."
Pima officials said after this letter, they had not further contact with Loughner.
So far, Loughner hasn't cooperated with authorities and has offered no motivation for the attack, reports CBS News correspondent Bob Orr. He is but isn't expected to say much, having invoked his 5th Amendment rights.
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Investigators said they carried out a search warrant at Loughner's home and seized a letter addressed to him from Giffords' congressional stationery in which she thanked him for attending a "Congress on your Corner" event at a mall in Tucson in 2007. Saturday's shooting occurred at a similar event.
Other evidence seized from his home included an envelope from a safe with messages such as " ," "My assassination" and the name "Giffords" next to what appears to be Loughner's signature. Police say he purchased the Glock pistol used in the attack in November.
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Loughner lives with his parents about a five-minute drive from the shootings, in a middle-class neighborhood lined with desert landscaping and palm trees.
Neighbors said Loughner kept to himself and was often seen walking his dog, almost always wearing a hooded sweat shirt and listening to his iPod.
His high school friends said they fell out of touch with Loughner and last spoke to him around March, when one of them was going to set up some bottles in the desert for target practice and Loughner suggested he might come along. It was unusual - Loughner hadn't expressed an interest in guns before - and his increasingly confrontational behavior was pushing them apart. He would send bizarre text messages, but also break off contact for weeks on end.
Several people who knew Loughner at community college said he did not engage in political discussions - in fact, he didn't talk much at all, and when he did classmates cringed.
"He made a lot of the people really uncomfortable, especially the girls in the class," said Steven Cates, who attended an advanced poetry writing class with Loughner at Pima Community College last spring. Though he struck up a passing friendship with Loughner, he said a group of other students went to the teacher to complain about Loughner at one point.
Another poetry student, Don Coorough, said Loughner read a poem about bland tasks such as showering, going to the gym and riding the bus in wild "poetry slam" style - "grabbing his crotch and jumping around the room."
When other students, always seated, read their poems, Coorough said Loughner "would laugh at things that you wouldn't laugh at." After one woman read a poem about abortion, "he was turning all shades of red and laughing," and said, "Wow, she's just like a terrorist, she killed a baby," Coorough said.
"He appeared to be to me an emotional cripple or an emotional child," Coorough said. "He lacked compassion, he lacked understanding and he lacked an ability to connect."
Cates said Loughner "didn't have the social intelligence, but he definitely had the academic intelligence."
"He was very into the knowledge aspect of school. He was really into his philosophy classes and he was really into logic and English. And he would get frustrated by the dumbed-down words people used in class," Cates said.
Lynda Sorenson, a 52-year-old who shared an algebra class with Loughner, painted a disturbing picture of the suspect in several e-mails to friends.
In one of the notes, provided to the Washington Post, Sorenson wrote:
"We have a mentally unstable person in the class that scares the living crap out of me. He is one of those whose picture you see on the news, after he has come into class with an automatic weapon. Everyone interviewed would say, Yeah, he was in my math class and he was really weird. I sit by the door with my purse handy. If you see it on the news one night, know that I got out fast..."
Loughner expressed his interest in grammar and logic on the Internet as he made bizarre claims - such as that the Mars rover and the space shuttle missions were faked.
He frequently used "if-then" constructions in making nonsensical arguments. For instance: "If the living space is able to maintain the crews life at a temperature of -454F then the human body is alive in the NASA Space Shuttle. The human body isn't alive in the NASA Space Shuttle. Thus, the living space isn't able to maintain the crews life at a temperature of -454F."
Loughner also said in one video that government is "implying mind control and brainwash on the people by controlling grammar." He described America's laws as "treasonous" and said that "every human who's mentally capable is always able to be treasurer of their new currency."
Loughner described himself as a U.S. military recruit in the video. A military official speaking on condition of anonymity said Loughner was rejected from the Army in 2008 because he . The official did not know what type of drug was detected in the screening.
In October 2007, Loughner was cited in Pima County for possession of drug paraphernalia, which was dismissed after he completed a diversion program, according to online records.
A year later he was charged with an unknown "local charge." That charge was also dismissed following the completion of a diversion program in March 2009, the Arizona Daily Star reported.
"He has kind of a troubled past, I can tell you that," Sheriff Clarence Dupnik said.