In messages left on the Internet before the shooting, Loughner, 22, revealed himself to be a social outcast with paranoid, nihilistic beliefs and a fixation with grammar.
At a public meeting with Congresswoman Gabrielle Giffords three years ago, he asked: "What is government if it doesn't exist?" It left the politician baffled.
According to the Southern Poverty Law Centre, a U.S. civil rights group, Loughner's language and beliefs appeared to resemble those of David Wynn Miller, a Milwaukee-based activist who believes the U.S. government uses grammar to control people's minds.
Miller, 62, a retired welder, has described himself as a plenipotentiary judge, ambassador, banker, genius and King of Hawaii, and invented his own form of grammar called "truth language", that is said to set people free of the government.
He said he was appalled by the shootings, but agreed with Loughner's pre-shooting Internet statement that
FBI agents combing through Loughner's life will also explore whether he was an enthusiast of the occult after a fake skull was found at his home, sitting in a plant pot with shrivelled oranges. It appeared to be some form of shrine.
The skull was concealed outside the home he shares with his parents, Amy and Randy, in a middle-class area. Classmates and neighbours described Loughner as "creepy" and "an emotional cripple" and said he used to ask teachers about mind control.
They said he was an atheist who also believed that NASA space shuttle missions, which have been flown by Miss Giffords's astronaut husband, Mark Kelly, were faked.
Ben McGahee, 28, a professor at Pima Community College, said:
Lynda Sorenson, 52, a mature student who had an algebra class with Loughner, wrote on email in June:
Loughner was suspended in September after writing on the Internet that the college was "unconstitutional".
On Monday, one of the people who jumped on Loughner as he tried to reload on Saturday told of the struggle with him. Patricia Maisch, 61, who grabbed his second magazine, said: "The woman next to me was shot and I was expecting to be next. Then two men knocked him over and somebody yelled, 'Get the gun!' so I knelt up.
Colonel Bill Badger, 74, one of those three men, was grazed by a bullet on the back of his head. "I grabbed him around the throat," the colonel said.