TUCSON, Ariz. - Authorities on Sunday charged a 22-year-old man described as a pot-smoking loner with trying to assassinate Rep. Gabrielle Giffords and killing others at a political event, revealing that he had scrawled on an envelope the words "my assassination" and "Giffords."

But the discoveries at his home in southern Arizona provided few answers to a shocked nation, from the victims of Saturday's shooting rampage to lawmakers worried about their safety: What motivated the rampage outside a supermarket that killed six and injured 14?

Giffords, 40, lay in intensive care at a Tucson hospital, after being shot in the head at close range. Doctors said she had responded repeatedly to commands to stick out her two fingers, giving them hope she may survive.

Court papers filed with the charges against Jared Loughner said he had previous contact with the Democratic lawmaker. The documents said he had received a letter from Giffords in which she thanked him for attending a "Congress on Your Corner" event at a mall in Tucson in 2007.

At that event, Giffords took a question from Loughner.

Angered by responseAccording to two of his high school friends the question was essentially: "What is government if words have no meaning?"

Loughner was angry about her response - she read the question and had nothing to say.

"He was like . . . 'What do you think of these people who are working for the government and they can't describe what they do? "' one friend told The Associated Press Sunday. "He did not like government officials, how they spoke. Like they were just trying to cover up some conspiracy."

Both friends spoke on condition of anonymity, saying they wanted to avoid the publicity surrounding the case.

The friends' comments paint a picture bolstered by other former classmates and Loughner's own Internet postings: that of a social outcast with nihilistic, almost indecipherable beliefs steeped in mistrust and paranoia.

"If you call me a terrorist then the argument to call me a terrorist is Ad hominem," he wrote Dec. 15 in a wide-ranging screed that was posted in video form and ended with this: "What's government if words don't have meaning?"

Collecting evidence

Investigators carrying out a search warrant at his parents' home in a middle-class neighborhood found an envelope in a safe with the words "I planned ahead," "My assassination" and the name "Giffords" next to what appears to be Loughner's signature.

An official familiar with the investigation said local authorities are looking at a possible connection between Loughner and an online group known for white supremacist, anti-immigrant rhetoric.

Meanwhile, transcripts of 911 emergency calls paint a frantic scene as bystanders called for help. In a tape of the call released by the Pima County Sheriff's Office, a person putting up a display for a pill bottling company was among the first to report the crime.

The caller says: "It's Giffords! There was a shooting at Safeway at Ina & Oracle where Gabrielle Giffords was. I do believe Gabby Giffords was hit. A guy had a semiautomatic pistol. He went in and just started firing and he ran."

Prosecutors charged Loughner with one count of attempted assassination of a member of Congress, two counts of killing an employee of the federal government and two counts of attempting to kill a federal employee. Loughner is expected to appear in court today.

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