After more than 48 hours of gathering evidence and conducting extensive interviews, authorities said today it was clear that many people knew Jared Lee Loughner was troubled before he allegedly killed six people and injured 14 others in an apparent assassination attempt on Arizona Rep. Gabrielle Giffords.
Pima County Sheriff Clarence Dupnik, whose office has been investigating Saturday's deadly shooting along with the FBI and other agencies, said that Loughner "has probably been troubled for some time."
"I don't think there is any doubt about that at all," he said. "I think the entire neighborhood where they lived was aware."
Dupnick also said Loughner came from a somewhat dysfunctional family. One neighbor said he got the impression something was wrong with the young man the first time he met him two months ago.
"I told my mother I thought he was a serial killer the first time I saw him," neighbor Jason Johnson told ABC News.
One college professor of Loughner's told ABC News the 22-year-old exhibited such bizarre behavior -- from random outbursts in class to scribbling disturbing notes on quizzes and tests -- that he feared for the other students' lives.
"There was one outburst when he just yelled, 'How can you deny math?'" Pima Community College mathematics professor Ben McGahee said. On a quiz, McGahee said Loughner wrote "Mayhem Fest" in large, bolded, capitol letters.
"I took that to mean mayhem, being craziness in the classroom... predicting a shooting. I don't want to be another Columbine or Virginia Tech," McGahee said, referring to two of the deadliest school shootings in U.S. history.
McGahee said "at least half a dozen" students came to him to express concern over Loughner, including multiple students that said they feared for their safety.
One of Loughner's classmates from another class, however, said he was quiet but seemed completely normal until early 2010 when he underwent a mysterious, radical change.
"I don't know what might have caused him to change, but from the way he was talking to me [online]... you can see," former classmate and longtime friend Tong Shan said. "It was just questions and questions and random, weird questions that didn't go together... He would just trip out."
"I don't know what the hell happened to him," she said.
Loughner was suspended from Pima Community College after several "disruptions" and the discovery of a YouTube video apparently made by Loughner in which he calls the school "illegal." The school said he would only be allowed back if he obtained "a mental health clearance indicating, in the opinion of a mental health professional, his presence at the College does not present a danger to himself or others." Instead, Loughner dropped out.
Loughner appeared in court for the first time today. Though six were killed and 14 others injured in the mass shooting, Loughner has been charged with two counts of murder – for the deaths of a federal judge and a member of Giffords' staff – and three counts of attempted murder. A 9-year-old girl was also killed in the attack.
Though she was shot in the head, Giffords, who police said was the target of the assault, survived.