The 22-year-old Loughner used his home computer to browse a website with information about the effects of lethal injection.
He appeared to want to know what death by injection felt like.
Lethal injection is the method of capital punishment imposed by the federal government.
Loughner also allegedly browsed the Internet for information about solitary confinement and, perhaps more disturbingly, an official said, he had been researching political assassins.
It all paints a dark picture of cold-blooded forethought, sources said, and an obsession with assassinating Rep. Gabrielle Giffords, D-Ariz., who was shot in the head but survived the attack.
Police previously released details about items confiscated from Loughner, including notes with the words, "I planned ahead," "Giffords," and "my assassination."
All evidence of cold-blooded premeditation.