This doesn 't prove anything one way or the other about Jared Loughner's mental health, but it does suggest that he was undertaking a political act:
In the weeks and days before the shooting rampage in Tucson, suspect Jared Lee Loughner surfed the Internet on his computer in what investigators believe was an effort to prepare for his alleged assassination attempt, law enforcement sources familiar with the investigation said.
Loughner pulled up several Web sites about lethal injections and solitary confinement in prison, said the sources, who asked to be anonymous because the investigation is ongoing. He also viewed Internet sites about political assassins, according to an analysis of Loughner's computer that was completed by investigators last week, the sources said.
Whether or not he is determined to have been legally sane, this does seem to indicate that it was not an accident that Giffords is a congresswoman. Whether or not it mattered that Giffords was a Democratic congresswoman is still unknown. But I think the fact that he knew he was contemplating a political assassination argues in favor of the idea that the violent rhetorical anti-government atmosphere may have contributed to his decision. In any case, this information indicates that the trial will have to address that so this issue won't be going away.