Tucson, Arizona (CNN) -- The 22-year-old man under arrest in Saturday's massacre in Arizona railed against government "mind control" and illiteracy in online missives and had "kind of a troubled past," as the local sheriff put it.
"There's reason to believe this individual may have a mental issue," Pima County Sheriff Clarence Dupnik told reporters Saturday night.
An Arizona law enforcement source and a U.S. law enforcement source have identified the suspect as Jared Lee Loughner, a 22-year-old former community college student. He was taken into custody after the massacre at a Tucson supermarket that killed a federal judge, a 9-year-old girl and four others and seriously wounded U.S. Rep. Gabrielle Giffords, who was hosting a meeting with constituents at the Safeway.
"Good-bye friends," read a Saturday morning posting on Loughner's MySpace page, just hours before the shooting. "Dear friends ... Please don't be mad at me. The literacy rate is below 5%. I haven't talked to one person who is literate."
And a December 30 posting read, "Dear Reader ... I'm searching. Today! With every concern, my shot is now ready for aim. The hunt, a mighty thought of mine."
Dupnik told reporters that the suspect had "kind of a troubled past" that included brushes wtih the law. Though he provided no details, he said, "We understand that there have been law enforcement contacts with the individual where he made threats."
Online, Loughner complained about the "second Constitution," a term legal scholars sometimes use to describe the post-Civil War amendments that ended slavery, extended the right to vote and required equal protection under the law. Its meaning to Loughner could not be clearly discerned.
"In conclusion, reading the second United States constitution I can't trust the current government because of the ratifications: the government is implying mind control and brainwash on the people by controlling grammar," he wrote in a Decmber 15 video message on YouTube. "No! I won't pay debt with a currency that's not backed by gold and silver! No! I wont trust in God!"
And in an apparent reference to Giffords' congressional district, he wrote, "The majority of people, who reside in District-8 are illiterate -- hilarious."
On his YouTube page, a list of his favorite books included both "Mein Kampf" and the "Communist Manifesto," along with works by George Orwell, Ray Bradbury, Ken Kesey, Herman Hesse, Ernest Hemingway, Plato and Aesop's Fables. But while the writer complained frequently about poor grammar and illiteracy, he wrote on MySpace on December 26 that he wouldn't correct his own errors. "I think the CIA watches my-space," he added.
Loughner dropped out of high school in 2006, after his junior year, said Tamara Crawley, a spokeswoman for the Marana United School District in suburban Tucson. Court records indicate he had been arrested for possession of drug paraphernalia in 2007, but the charge was dismissed.
In 2008, he tried to enlist in the U.S. Army. The Army rejected him, and privacy laws keep the military from disclosing the reason, the service said in a statement to CNN.
He also enrolled at Aztec Middle College, a partnership between Tucson schools and Pima Community College that helps high school dropouts transition to community colleges, PCC President Sylvia Lee told CNN. He took classes at the college from 2005 until October 2010, when withdrew after five contacts with police "for classroom and library disruptions" at two campuses between February and September, the school said in a statement issued Saturday night.
Loughner was suspended after authorities found a YouTube video in which he called the school "illegal according to the U.S. Constitution, and makes other claims," the PCC statement said. He quit during an October 4 meeting with his parents and school administrators, and a follow-up letter warned that to return, he had to present a doctor's note stating that "his presence at the College does not present a danger to himself or others."
CNN's Emily Smith, Barbara Starr, Thelma Gutierrez and Matt Smith contributed to this report.