9:58 a.m. -- Giffords posts message on Twitter inviting constituents to event at the Safeway supermarket in Tucson.
10:00 a.m.-- Town hall meeting begins.
10:10 a.m. -- Gunman opens fire.
10:11 a.m. -- First 911 call is received
10:19 a.m. -- 6-member rescue crew arrives.
10:22 a.m. -- Suspect in police custody.
10:24 a.m. -- Wounded victims removed from the scene.
2:46 p.m. -- President Obama addresses the nation in response to the shooting.
3:00 p.m. -- Police announce a second person may be involved in the shooting.