Federal law enforcement officials were poring over versions of a MySpace page that belonged to Loughner and over a YouTube video published weeks ago under an account "Classitup10" and linked to him. The MySpace page, which was removed within minutes of the gunman being identified by officials, included a mysterious "Goodbye friends" message published hours before the shooting and exhorted his friends to "Please don't be mad at me."
In one of several Youtube videos, which featured text against a dark background, Loughner described inventing a new U.S. currency and complained about the illiteracy rate among people living in Giffords' congressional district in Arizona.
Story: Profile of suspect Jared Loughner: ‘I can't trust the current government'
"I know who's listening: Government Officials, and the People," Loughner wrote. "Nearly all the people, who don't know this accurate information of a new currency, aren't aware of mind control and brainwash methods. If I have my civil rights, then this message wouldn't have happen (sic)."
Giffords spokesman C.J. Karamargin said three Giffords staffers were shot. Two are expected to survive, but Gabe Zimmerman, a former social worker who served as Giffords' director of community outreach, was killed.
Giffords had worked with the judge in the past to line up funding to build a new courthouse in Yuma, and Obama hailed him for his nearly 40 years of service as a judge.
Roll, a married father of three children, was the chief judge in Arizona, appointed in 1991 by the first President Bush, NBC News reported.
"The devoted husband, father of three, grandfather of five, and friend to all who knew him, will be greatly missed by his family and community," said a statement released by the U.S. District Court for the District of Arizona. "He was a warm, compassionate judge and inspirational leader in what is one of the busiest districts in the country."
An uncle of the 9-year-old girl told the Arizona Republic Saturday evening that a neighbor was going to the event and invited Green along because she had just been elected to the student council and was interested in government.
"The next thing you know this happened. How do you prepare for something like this? My little niece got killed — took one on the chest and she is dead," Greg Segalini told a reporter for the Arizona newspaper.
'Gabby'
Giffords was first elected to Congress amid a wave of Democratic victories in the 2006 election, and has been mentioned as a possible Senate candidate in 2012 and a gubernatorial prospect in 2014.
Giffords is married to astronaut Mark E. Kelly, who has piloted space shuttles Endeavour and Discovery. The two met in China in 2003 while they were serving on a committee there, and were married in January 2007. NBC News reported that Kelly flew to Tucson on a NASA aircraft after the shooting.
Sen. Bill Nelson, chairman of the Senate Commerce Space and Science Subcommittee, said her husband is training to be the next commander of the space shuttle mission slated for April. His brother is currently serving aboard the International Space Station, Nelson said.
'Chaos, people screaming, crying'
The shooting occurred at a shopping center called La Toscana Village as Giffords met with voters outside a Safeway grocery store.
Giffords, known as "Gabby," tweeted shortly before the shooting, describing her "Congress on Your Corner" event: "My 1st Congress on Your Corner starts now. Please stop by to let me know what is on your mind or tweet me later."
"It's not surprising that today Gabby was doing what she always does, listening to the hopes and concerns of her neighbors," Obama said. "That is the essence of what our democracy is about."
Mark Kimball, a communications staffer for Giffords, described the scene as "just complete chaos, people screaming, crying." The gunman fired at Giffords and her district director and started shooting indiscriminately at staffers and others standing in line to talk to the congresswoman, Kimball said.
Video: Rep. Giffords respected for political skill, warmth (on this page)
"He was not more than three or four feet from the congresswoman and the district director," he said.
Law enforcement officials and reporters from around the country quickly descended on Tucson, the second biggest city in the state and home to the University of Arizona. The scene has been converted into a command post with about a dozen or so emergency vehicles and agents in FBI jackets milling about the location.
Outside Giffords' office on Capitol Hill, a handful of congressional staffers could be seen walking into her office without comment, some with roller bags and one who was in tears. About a half dozen yellow flowers placed by one mourner sat outside the door.
'We are freaked out'
In Loughner's middle-class neighborhood — about a five-minute drive from the scene — sheriff's deputies had much of the street blocked off as curious neighbors asked what was going on. The neighborhood sits just off a bustling Tucson street and is lined with desert landscaping and palm trees.
Neighbors said Loughner kept to himself but that they often saw him walking his dog, almost always wearing a hooded sweat shirt listening to his iPod. Neighbors said Loughner lived with his parents.
"We're getting out of here. We are freaked out," 33-year-old David Cleveland, who lives a few doors down from Loughner's house, told The Associated Press.
Cleveland said he was taking his wife and children, ages 5 and 7, to her parent's home when they heard about the shooting.
"When we heard about it we just got sick to our stomachs," Cleveland said. "We just wanted to hold our kids tight."
High school classmate Grant Wiens, 22, said Loughner seemed to be "floating through life" and "doing his own thing."
"Sometimes religion was brought up or drugs. He smoked pot, I don't know how regularly. And he wasn't too keen on religion from what I could tell," Wiens said.
Tyler Ramsier, who graduated from Mountain View High School a year before Loughner, told the Arizona Republic that Loughner dressed in dark clothes.
Dangerous threats
The shooting comes amid a highly charged political environment that has seen several dangerous threats against lawmakers but nothing that reached the point of actual violence.
Video: An outpouring of grief in stricken Tucson (on this page)
A San Francisco man upset with House Speaker Nancy Pelosi's support of health care reform pleaded guilty to threatening the Democratic congresswoman and her family, calling her directly on March 25 and threatening to destroy her Northern California home if she voted for health care reform.
In July, a California man known for his anger over left-leaning politics engaged in a shootout with highway patrol officers after planning an attack on the ACLU and another nonprofit group. The man said he wanted to "start a revolution" by killing people at the ACLU and the Tides Foundation.
Giffords is known in her southern Arizona district for her numerous public outreach meetings, which she admitted in an October interview with The Associated Press can sometimes be challenging.
"You know, the crazies on all sides, the people who come out, the planet earth people," she said with a following an appearance with Adm. Mike Mullen in which the chairman of the Joint Chiefs of Staff was peppered with bizarre questions from an audience member. "I'm glad this just doesn't happen to me."
NBC News, The Associated Press and Reuters contributed to this report.
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