Investigators carried out a search warrant at the suspect's home and seized an envelope from a safe with messages such as "I planned ahead," "My assassination," and the name "Giffords" next to what appears to be the man's signature.
The FBI also found a letter in a safe from Giffords, on Congressional stationery, dated Aug. 30, 2007 that thanked Loughner for attending a "Congress on your Corner" event at the Foothills Mall in Tucson.
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 killing a federal employee.
Heather Williams, the first assistant federal public defender in Arizona, says the 22-year-old suspect doesn't yet have a lawyer, but that her office is working to get a lawyer appointed for Loughner.
Loughner remains in federal custody and is being transported to Phoenix where he will make an initial court appearance on Monday at 2 p.m. local time.
Meanwhile, authorities released 911 calls in which a person witnessing the mass shooting outside a grocery store in Tucson describes a frantic scene and says, "I do believe Gabby Giffords was hit."
Loughner fired at Giffords' district director and shooting indiscriminately at staffers and others standing in line to talk to the congresswoman, said Mark Kimble, a communications staffer for Giffords.
"He was not more than three or four feet from the congresswoman and the district director," Kimble said, describing the scene as "just complete chaos, people screaming, crying."
Loughner is accused of killing six people, including a federal judge, an aide to Giffords and a 9-year-old girl who was born on Sept. 11, 2001. Fourteen others were wounded, including the three-term Democrat lawmaker. Authorities don't know his motive, but said he targeted Giffords at a public gathering around 10 a.m. Saturday.
Doctors treating the lawmaker provided an optimistic update about her chances for survival, saying they are "very, very encouraged" by her ability to respond to simple commands along with their success in controlling her bleeding.
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.
"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)."
In Loughner's middle-class neighborhood - about a five-minute drive from the scene - sheriff's deputies had much of the street blocked off. The neighborhood sits just off a bustling Tucson street and is lined with desert landscaping and palm trees.
Neighbors said Loughner lived with his parents and kept to himself. He was often seen walking his dog, almost always wearing a hooded sweat shirt and listening to his iPod.