'Vitriol' Cited As Possible Factor In Arizona Tragedy : NPR

A second person of interest:

At a news conference Saturday night, a clearly emotional Dupnik, who has been close to both Giffords and Roll, repeatedly cited what he characterized as the "vitriol" that has infected political discourse. He said that his own state has become "the mecca for prejudice and bigotry."

There is reason to believe, he said, that the shooting suspect "may have a mental issue," adding that people like that "are especially susceptible to vitriol."

"That may be free speech, but it's not without consequences," he said.

The suspected gunman was tackled and held by people at the event until police arrived and took him into custody. Law enforcement sources told NPR the suspect was 22-year-old Jared Lee Loughner.

Dupnik declined to name the suspect, but said he "has kind of a troubled past — I can tell you that — and we are not convinced he acted alone."

Officials have a photograph of a second "person of interest," a 50-year-old white male, Dupnik said. "We have an individual we are actively in pursuit of, but I cannot tell you who he is at this point," the sheriff said.