Jan. 9, 2011  -- A longtime friend of Jared Lee Loughner, the suspect in custody following the murder of six people in an apparent assassination attempt on Arizona Rep. Gabrielle Giffords, said there was a mysterious, significant change in him a year before the shooting.

"He was a good person that just somehow changed so much," former classmate and friend Tong Shan told ABC News in an exclusive interview. "I don't know what the hell happened to him."

When she heard news reports of Loughner's arrest in connection with the deadly attack, she said, "I was shocked, but I believed it was him."

According to court documents released today, authorities discovered a safe in Loughner's home with a thank you letter from Giffords for attending a Congress on Your Corner event in 2007 -- the same kind of event Loughner allegedly assaulted Saturday. Another envelope said "I planned ahead," "My assassination" and "Giffords" and bore what appears to be Loughner's signature, the documents said.

Shan said she became friends with Loughner the day the two graduated from high school and also had class together at Pima Community College in 2007. She said the they would hang out often after class but lost touch after the semester ended until they reconnected in the summer of 2010 when, Shan said, Loughner acted radically different.

"I don't know what might have caused him to change, but from the way he was talking to me [online]... you can see. It was just questions and questions and random, weird questions that didn't go together," she said. "He wanted to know everything... He would just trip out.

"I don't know why it didn't jump out at me, like, 'Hey, something's wrong."

Shan last spoke to Loughner in October, after he was suspended and dropped out of school and before he purchased a semi-automatic handgun from a gunshop in Tucson. But she said while Loughner was "anti-government," he was never violent and never mentioned plans to buy a gun.

When he was suspended from Pima Community College, the school sent a letter to Loughner's parents stating that if Loughner wished to return to the school, he would have to "obtain a mental health clearance indicating, in the opinion of a mental health professional, his presence at the College does not present a danger to himself or others," the school said in a statement.

Loughner: 'Classroom And Library Disruptions'

One Pima Community College student, who had a poetry class with Loughner later in his college career, said he would often act "wildly inappropriate."

"One day [Loughner] started making comments about terrorism and laughing about killing the baby," classmate Don Coorough told ABC News, referring to a discussion about abortions. "The rest of us were looking at him in shock ... I thought this young man was troubled."

Another classmate, Lydian Ali, recalled the incident as well.

"A girl had written a poem about an abortion. It was very emotional and she was teary eyed and he said something about strapping a bomb to the fetus and making a baby bomber," Ali said.

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."

Exclusive: Suspected Shooter's Poetry Hints at Loneliness

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.

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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.