Pima County Sheriff Clarence Dupnik, who only identified the shooter as a 22-year-old white male, said the evidence online and information they've received from two schools that Loughner attended led him to believe the gunman was "unstable."
"There's reason to believe that this individual may have a mental issue," Dupnik told reporters today. "I'm not a psychiatrist so I have no reason to believe the person was insane. Was he unstable? I would agree with that."
In poetry written by Loughner for a class at the college and obtained exclusively by ABC News, he discusses being confused and detached from others.
"Looking around, the cute women are catching my eye, probably waiting for their hot boyfriends wandering in the locker room," one poem, entitled Meat Head, reads. "Confused look on my face of no idea what to do, deciding to copy other men's routines..."
In another poem entitled "Dead as a dodo.", Loughner describes a serene, but somber scene at a cemetery. "The full moon slowly setting for the sun is rising. At the local cemetery there is weeping. The dodo is finally deing [sic]," it reads.
In one of many YouTube videos apparently created by Loughner, he reads the poetry aloud. In other videos, he rants against the government, low literacy rates and what he sees as false currency.
"Hello, my name is Jared Lee Loughner. This video is my introduction to you!" one video, uploaded Dec. 15, says. "My favorite activity is conscience dreaming; the greatest inspiration for my political business information. Some of you don't dream -- sadly... My ambition -- is for informing literate dreamers about a new currency; in a few days, you know I'm conscience dreaming! Thank you!"
In another video, he accuses the government of mind control via grammar.
"In conclusion, reading the second United States Constitution, I can't trust the current government because of the ratifications: The government is implying mind control and brainwash on the people by controlling grammar. No! I won't pay debt with a currency that's not backed by gold and silver! No! I won't trust in God!" it says.
In the YouTube profile, the account holder, identified as Loughner, lists "The Communist Manifesto" and "Mein Kampf" among his favorite books.
Despite being shot in the head, Congresswoman Giffords survived the attack and doctors said Saturday they were "optimistic" about her recovery. Federal judge John Roll, a 9-year-old girl and a member of Giffords' staff were killed in the attack. The staff member, Gabe Zimmerman, was Giffords' director of community outreach.
Loughner has been charged on three counts of attempted murder as well as two counts of murder for the deaths of Zimmerman and Roll.
ABC News' Elisa Roupenian contributed to this report.