"We're not convinced that he acted alone," Dupnik said of the suspect officials have in custody. "There is some reason to believe that he came to this location with some other individual."
Dupnik said law enforcement is "actively in pursuit of" of a certain individual, but that the person was only a "person of interest," and not a suspect, thus far.
At the news conference, law enforcement officials declined to identify the suspect in custody. Dupnik described the person as a 22-year old white male with a "criminal background" and "kind of a troubled past."
"There have been law enforcement contacts with the individual over he made threats [sic]," Dupnik said, adding that the threats were "to kill."
Media reports have identified the suspect as Tucson resident Jared Loughner, and internet searches turned up YouTube videos apparently made by Loughner in which he writes about government "mind control" and "brainwashing."
The shooting occurred in the parking lot of a Safeway in Tucson where Giffords was hosting a "Congress on Your Corner" event. The first 911 call came in at 10:11 AM local time. Among the people confirmed to have been killed in the shooting is Lower Federal Judge John Roll. Dupnik told reporters that the judge, a friend of Giffords, had decided to stop by the event after going to Mass nearby this morning. Roll, Dupnik said, was simply "in wrong place at the wrong time." Giffords was a different matter.
"I think, yes, she was the target," Dupnik said.
The sheriff spent several minutes directing his anger at the "vitriol" he said comes from radio and television personalities. "That may be free speech, but its not without consequences," Dupnik said.
"I hope that are all Americans are as saddened and as shocked as we are," he said. "We need to do a little soul searching."
Arizona in particular, he said, has "become the mecca for prejudice and bigotry."
Despite the tragedy of the day's events, Dupnik made a point of crediting "two brave individuals" with tackling the shooter while there were still bullets in the gun he was firing. Had he not been tackled, the sheriff said law enforcement believes it "may be a possibility" that the shooter planned to kill himself.
Captain Chris Nanos with the Pima County Sheriff's Department said that Congresswoman Giffords was shot in the head at "very close" range, although officials would not say if she was the first person shot.
The final speaker was Dr. Richard Carmona, former U.S. Surgeon General, who spoke about Giffords' medical condition.
"This is going to take a little while, to see how she does after her surgery," he said. "I saw what was done, I know the surgery that was done, with guarded optimism, I hope that she will survive."
"But this is a very devastating wound," he added.
Carmona said it was "hard to say" what, if any, brain damage Giffords may have sustained. The doctors who performed the surgery on Giffords today are expected to address the media tomorrow.