NYT says it was a plot

U.S. Cites Evidence of Assassination Plot

Possible second suspect was only a taxi driver who followed Loughner into the supermarket when he didn't have sufficient change to pay for the cab.

Court documents  state event was caught on videotape.

"...evidence seized from Mr. Loughner’s home showed that he had planned to kill Representative Gabrielle Giffords, who was in critical condition with a gunshot wound to the head. Found in Mr. Loughner’s home, F.B.I. special agent Tony M. Tayler Jr. said in an affidavit supporting the charges, was an envelope with the handwritten words, "I planned ahead," "My assassination," and "Giffords."