Three-term Arizona congresswoman Gabrielle Giffords is in critical condition with a gunshot wound to the head after a shooting that killed six people outside a supermarket.
Police say the gunman targeted Giffords as she met with constituents. Arizona's chief federal judge and a nine-year-old girl are among the dead.
Pima County Sheriff Clarence Dupnik describes suspect Jared Loughner as mentally unstable and possibly acting with an accomplice. Authorities say the gun used was legal.
There was further tension at a vigil later outside Giffords' office when a loud noise was heard. But authorities investigating a suspicious package say there was nothing explosive and the noise was caused by efforts to destroy the package and render it safe.
There's been an outpouring of outrage, sadness and condolences from officials, including Arizona Gov. Jan Brewer and President Barack Obama.