Gabrielle Giffords Gabrielle Giffords

U.S. Rep. Gabrielle Giffords remained in critical condition Sunday after she was shot in the head in Tucson, Ariz., and the Pima County sheriff blamed angry political discourse, in part, for the shooting.

Giffords, 40, was one of 18 people shot — six killed, 12 wounded — during a shooting at a constituent meeting outside a Safeway grocery store. She underwent surgery Saturday afternoon for a gunshot wound to the head.

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As of early Sunday, Giffords was able to communicate with doctors with simple commands.

"We are very encouraged by that," Dr. Michael Lemole, Jr., chief of neurosurgery at Tucson's University Medical Center, said at a news conference Sunday. "I am cautiously optimistic."

Law enforcement officials confirmed the identity of the suspected gunman as 22-year-old Jared Lee Loughner. The Pima County Sheriff's Department said he had been transferred to FBI custody. He is due in court Monday on five charges — trying to kill Giffords and two of her aides, and murdering U.S. District Judge John Roll and Gifford aide Gabe Zimmerman, 30. State charges will be filed at a later date.

The motive for the shooting remains unclear and Loughner has refused to speak under his right to protect himself against self-incrimination. The suspect had spoken out against government "mind control" and had "kind of a troubled past," said Pima County Sheriff Clarence Dupnik. "There's reason to believe this individual may have a mental issue."

However, Dupnik also pointed to "vitriolic rhetoric" stemming from political debates.

"When you look at unbalanced people, how they respond to the vitriol that comes out of certain mouths about tearing down the government, the anger, the hatred, the bigotry that goes on in this county is getting to be outrageous. Unfortunately, Arizona, I think, has become sort of the capital," he said. "We have become the mecca for prejudice and bigotry."

Giffords faced anger over her support of the health care reform last year, and had her office vandalized the day the House approved the bill.

President Barack Obama announced Saturday that Roll was among those killed during the shooting. Nominated by George H.W. Bush, Roll joined the District Court in 1991. He served as a chief judge from 2006 until his death.

Obama released a statement Saturday calling the shooting an "unspeakable tragedy" and that "such a senseless and terrible act of violence has no place in a free society."

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Giffords was one of two Arizona members of Congress to whom MSNBC host Keith Olbermann made campaign contributions last year, prompting network President Phil Griffin to suspend him for five days without pay in November.

A Democrat first elected to office in 2006, Giffords is married to Navy Capt. Mark Kelly, a NASA astronaut who's scheduled to go on a shuttle mission to the International Space Station.

Giffords is also a cousin of Gwyneth Paltrow. "Although I have never had the pleasure of meeting Congresswoman Giffords, my thoughts and prayers are with her and her family as well as the other victims of this horrible act of senseless violence," Paltrow said in a statement to Entertainment Tonight.

Among the victims was a 9-year-old girl born Sept. 11, 2001. For that reason, Christina-Taylor Green was in a book titled called Faces of Hope, which featured one baby from each state born on the day terrorists killed nearly 3,000 people.

The Associated Press reported that she was a member of the student council at her school and was there because she was interested in government. She's also the granddaughter of former major league manager Dallas Green and the second cousin of One Tree Hill's Sophia Bush.

The other victims included two 76-year-olds and a 79-year-old.