"We’re not convinced that he acted alone," he said at a news conference at Westward Look resort.
He confirmed that there were 19 people injured and that six people are dead.
He also refused to identify any suspects, although the name of shooter Jared Lee Loughner has been widely reported.
He said that two "brave individuals" tackled the shooter, and that Roll was in the wrong place at the wrong time, as he'd simply shown up to say hello to his friend Giffords.
Update: He said a semi-automatic weapon was used and that all 19 victims were shot.
He also angrily denounced the vitriolic political climate of today—especially in Arizona.
"We have become the Mecca for prejudice and bigotry," he said.