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.