22-year-old Arizona shooting suspect Jared Lee Loughner planned ahead. According to court documents, police found evidence of an assassination plot against Rep. Gabrielle Giffords at Loughner's house, including a 2007 letter from Giffords herself.
The letter thanked Loughner for attending a Giffords event and was found stashed in a safe in his house. From the criminal complaint:
According to former high school classmate Caitie Parker, Loughner was fuming after his encounter with Giffords at the 2007 "Congress on Your Corner"—the same kind of event Giffords was holding when she and 19 others were shot yesterday. Loughner "asked her a question, and he told me she was 'stupid and unintelligent,'" Parker said.
A friend recalled the meeting in the Wall Street Journal:
Mr. Loughner said he asked the lawmaker, "How do you know words mean anything?"... Mr. Loughner was "aggravated" when Ms. Giffords, after pausing for a couple of seconds, "responded to him in Spanish and moved on with the meeting."
This brief, weird exchange may have made an outsized impression on Loughner.