The two teenagers were in an old minivan just before midnight, driving through their scrubby neighborhood on the outskirts of Tucson when they were pulled over by sheriff's deputies. The driver and his passenger, Jared Lee Loughner, both smelled strongly of pot. It was the eve of Loughner's 19th birthday. Deputies cited him for possessing drug paraphernalia, his first criminal charge as an adult.

Between that stop Sept. 9, 2007, and Jan. 8 of this year — the day he was arrested as a suspect in shootings that killed six and wounded 13, including U.S. Rep. Gabrielle Giffords, outside a Safeway store in Tucson — Loughner frequently acted and sounded like a young man in need of mental health intervention.

He'd been kicked out of school, was rejected by the Army and struggled to find work. He was fired from a volunteer job at an animal shelter. His Internet postings were hostile and incoherent, with certain themes repeated — a distrust of government and his college, the Constitution, illiteracy and "lucid dreaming." He alienated fellow players in an online game with disjointed, hostile posts, including one in which he called the physicist Stephen Hawking a "freaking retard" and equated rape with sex.

Interviews with friends, teachers and classmates, and reviews of school documents and law enforcement reports — plus Loughner's own writings and comments — depict a young man's downward spiral, slow at first, accelerating dramatically a year ago, and culminating with his arrest on suspicion of murder eight days ago.

With so many danger signs, so many people having taken note of his deteriorating state, the haunting question for authorities and those close to Loughner is whether something could have been done to head off the tragedy. The record shows that attempts to intervene focused on his behavior, not on what caused it. As far as is known, Loughner never received professional help.

More than three years ago, those who knew him began to notice unsettling changes.

In August 2007, Loughner had shown up at a Giffords event and asked her a question. He told George Osler, the father of a childhood friend, that he was not satisfied with his congresswoman's response.

"He thought that she was fake," Osler said.

An old friend, Bryce Tierney, recently told Mother Jones magazine what Loughner had asked: "What is government if words have no meaning?"

Michelle Montanaro, a second-grade teacher and mother of Jared's onetime best friend Alex Montanaro, said that during a 2007 visit to their home, Loughner spoke excitedly about becoming a writer and told an indecipherable story about an angel talking to a reporter after the end of the world. "I didn't really understand it," Montanaro said. "Neither did Alex. We just sort of looked at each other."

Loughner, an only child, was born Sept. 10, 1988. His mother, Amy, in her early 50s, is a manager at Agua Caliente Park on the east side of Tucson. His father, Randy, 58, used to work as a carpet layer and pool surfacer, but has not worked recently, neighbors said. The Loughners' 1,400-square-foot brick home, landscaped with mesquite and saguaro cactus, was purchased in 1977 and has a county-assessed value of $105,000.

The Loughners are very private, neighbors said.

"They're like a mountain man. They want to be alone," said neighbor Wayne Smith, who broke the news of their son's arrest to the couple.

At Tortolita Middle School, Loughner was a normal boy whose passions reflected the times, friends said.

"He'd be at every popular block party," said Lela Chavis, 22, who bonded with him over music in their choir class. He was a considerate friend who would call her about class work if she missed school, she said.

Loughner was a talented tenor saxophone player with a taste for jazz, but he also liked the punk bands Rancid and the Misfits, and played in a garage band, friends said.

His favorite books, listed on his MySpace page, include classics such as "Animal Farm," "Brave New World" and "To Kill a Mockingbird," and political tracts such as "Mein Kampf" and "The Communist Manifesto."

An eighth-grade photo shows Loughner with bangs and small, roundish, wire-rimmed glasses. That prompted some classmates to call him Harry Potter, and once someone taped a "kick me" sign on his back, according to the Washington Post.

At Mountain View High School, Loughner was "very sweet, caring and kind, had no interest in drugs or alcohol, and had a big interest in music," said his girlfriend at the time, Kelsey Hawkes, now a junior at the University of Arizona. "He didn't start acting differently until after we had been broken up."