UPDATED: U.S. Representative Gabrielle Giffords, D-AZ, is fighting for her life following surgery for a gunshot wound to the head, sustained Saturday morning at a constituent event in Tucson. Her surgeon, Dr. Peter Rhee of University Medical Center, said, I am very optimistic about her condition.

Giffords was one of 18 people shot, at least six of whom are dead, when an assailant opened fire outside a grocery store as the Democratic lawmaker met with constituents on Saturday morning in Tucson, according to published reports.

One of the dead was an aide to the Congresswoman, Giffords spokesman C.J. Karamargin told the press. Reports say that other fatalities included a nine-year-old girl and a federal judge, John Roll.

Five of the wounded are still in critical condition, authorities said.

Giffords was hold a Congress on Your Corner event to listen to constituent concerns, her office said.

Authorities have the shooter in custody, a 22-year-old white man, Jared Lee Loughner, who reportedly posted quasi-incoherent messages on YouTube prior to the shooting that says, in part, that he cannot trust the federal government, which he calls treasonous and accuses of practicing mind control. The message also says he cannot trust in monetary systems not based on gold and silver.

Police have recovered a 9 mm semi-automatic weapon, authorities said.

Giffords was shot at point blank range, authorities said. At a recent press briefing, authorities said that the Congresswoman is unconscious but that the prognosis for her survival is good. She is at University Medical Center in Tucson.

Giffords, 40, was narrowly elected to her third term in the House of Representatives in November, defeating Republican and Tea Party favorite Jess Kelly by just 4,000 votes out of nearly 300,000 cast.

Her district encompasses the southeastern part of the state. It includes all of Cochise County and parts of Pima, Pinal, and Santa Cruz counties.

She drew criticism from the right during her campaign for her vote in favor of healthcare reform and her positions on immigration.

Her husband is U,S, astronaut Mark Kelly.

Jeff Rogers, Pima County Democratic Party Chairman, told the press that shots had been fired at a Giffords campaign office during the campaign. No one was hurt in that incident.

President Obama issued this statement:

This morning, in an unspeakable tragedy, a number of Americans were shot in Tucson, Arizona, at a constituent meeting with Congresswoman Gabrielle Giffords.  And while we are continuing to receive information, we know that some have passed away, and that Representative Giffords is gravely wounded. 

We do not yet have all the answers.  What we do know is that such a senseless and terrible act of violence has no place in a free society.  I ask all Americans to join me and Michelle in keeping Representative Giffords, the victims of this tragedy, and their families in our prayers.

Obama has dispatched FBI chief Robert Mueller to Arizona to take part in the investigation.

I was deeply horrified to learn today of the shooting of Representative Gabrielle Giffords and others in Tucson, said Speaker of the House John Boehner, R-OH. Our thoughts and prayers are with Congresswoman Giffords and her family, her staff, and the residents of Tucson on this sad day.   As this serious situation continues to develop, I remain in close communication with leaders of both parties, the Speaker's office and the Sergeant at Arms.  We will remain in constant communication regarding any schedule changes.