TUCSON, Ariz. - Federal prosecutors brought charges Sunday against the gunman accused of attempting to assassinate Rep. Gabrielle Giffords and killing six people at a political event in Arizona.

Investigators said they carried out a search warrant at Jared Loughner'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. He allegedly purchased the Glock pistol used in the attack in November at Sportsman's Warehouse in Tucson.

Court documents also show that Loughner had contact with Giffords in the past. Other evidence included a letter addressed to him from Giffords' congressional stationery in which she thanked him for attending a "Congress on your Corner" event at a mall in Tucson in 2007.

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 one appointed. Williams' office is asking for an outside attorney because one of those killed was U.S. District Judge John M. Roll.

Pima County Sheriff Clarence Dupnik said Sunday that Loughner acted alone.

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 shot 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 an aide to Giffords and a 9-year-old girl who was born on Sept. 11, 2001. Fourteen others were wounded. Authorities don't know Loughner's motive, but said he targeted Giffords at a public gathering around 10 a.m. Saturday.

Mourners crammed into the tiny sanctuary of Giffords' synagogue in Tucson to pray that she quickly recovered. Outside the hospital, candles flickered at a makeshift memorial. Signs read "Peace + love are stronger," ''God bless America and "We love you, Gabrielle."

People also laid down bouquets of flowers, American flags and pictures of Giffords.

One of the victims was Christina Taylor Green, who was a member of the student council at her local school and went to the event because of her interest in government. She is the granddaughter of former Philadelphia Phillies manager Dallas Green.

She was born on 9/11 and featured in a book called "Faces of Hope" that chronicled one baby from each state born on the day terrorists killed nearly 3,000 people.

The fact that Christina's life ended in tragedy was especially tragic to those who knew her. "Tragedy seems to have happened again," said the author of the book, Christine Naman. "In the form of this awful event."

Authorities said the dead included Roll; Green; Giffords aide Gabe Zimmerman, 30; Dorothy Morris, 76; Dorwin Stoddard, 76; and Phyllis Schneck, 79. Judge Roll had just stopped by to see his friend Giffords after attending Mass.

An unidentified man who authorities earlier said might have acted as an accomplice was cleared Sunday of any involvement. Pima County sheriff's deputy Jason Ogan told The Associated Press on Sunday that the man was a cab driver who drove the gunman to the grocery store outside of which the shooting occurred.

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.

The assassination attempt left Americans questioning whether divisive politics had pushed the suspect over the edge.

Giffords faced frequent backlash from the right over her support of the health care reform last year, and had her office vandalized the day the House approved the landmark measure.

Dupnik lashed out at what he called an excessively "vitriolic" atmosphere in the months leading up to the rampage as he described the chaos of the day.

The sheriff said the rampage ended only after two people tackled the gunman. A third person intervened and tried to pull a clip away from Loughner as he attempted to reload, the sheriff said.

"He was definitely on a mission," according to event volunteer Alex Villec, former Giffords intern.