Investigators carrying out a search warrant at his parents' home in a middle-class neighborhood found an envelope in a safe with the words "I planned ahead," "My assassination" and the name "Giffords" next to what appears to be his signature.
Neighbors said Loughner kept to himself and was often seen walking his dog, almost always wearing a hooded sweat shirt and listening to his iPod.
Comments from friends and former classmates bolstered by Loughner's own Internet postings have painted a picture of a social outcast with almost indecipherable beliefs steeped in mistrust and paranoia.
"If you call me a terrorist then the argument to call me a terrorist is Ad hominem," he wrote Dec. 15 in a wide-ranging posting.
Two high school friends said they had fallen out of touch with Loughner and last spoke to him around March, when one of them was going to set up some bottles in the desert for target practice and Loughner suggested he might come along. It was unusual -- Loughner hadn't expressed an interest in guns before -- and his increasingly confrontational behavior was pushing them apart. He would send bizarre text messages, but also break off contact for weeks on end.
"We just started getting sketched out about him," the friend said.
Around the same time, Loughner's behavior also began to worry officials at Pima Community College, where Loughner began attending classes in 2005, the school said in a release.
Between February and September, Loughner "had five contacts with PCC police for classroom and library disruptions," the statement said. He was suspended in September after college police discovered a YouTube video in which Loughner claimed the college was illegal according to the U.S. Constitution.
He withdrew voluntarily the following month, and was told he could return only if, among other things, a mental health professional agreed he did not present a danger, the school said.
Police said he purchased the Glock pistol used in the attack at Sportsman's Warehouse in Tucson in November.