Politico adds that Zimmerman was 30 years old, and had worked for Giffords since 2007.
Giffords was shot in the head, and 18 other people were injured, at a "Congress on Your Corner" event in the parking lot of a Safeway in Tucson this morning. There are conflicting reports as to the total number of people killed, but among the confirmed dead are Federal Judge John Roll and a 9-year old girl. One suspect, 22-year-old Jared Loughner, is in custody. Giffords underwent surgery today, and a doctor told the media this afternoon that he was 'very optimistic' about her recovery.