He tried to enlist in the Army in 2008 but was rejected as unqualified. And those who knew him described him to reporters as a "troubled young man" who frequently had such unusual outbursts that no one even wanted to sit next to him in class.
But, according to The Washington Post, on Nov. 30, Loughner legally purchased the Glock 19 semiautomatic pistol that law enforcement officials say he used to shoot U.S. Rep. Gabrielle Giffords at an event Saturday outside a busy supermarket in Tucson, Ariz., killing one of her aides, a federal judge, a 9-year-old girl and three retirees.
And that has revived the debate about gun ownership laws throughout the nation, but particularly in Arizona, which has some of the weakest gun control laws in the country. State laws there permit any law-abiding citizen over age 18 to buy a gun.
"At some point we need to ask the question: How did this man with this history of mental instability end up with this weapon," Senate Majority Whip Dick Durbin, D-Ill., said on CNN's "State of the Union" today.
"How did he go through the process and end up with this gun and this ammunition?"
Federal law enforcement officials told the Post that the semiautomatic pistol was fitted with a magazine that held about 30 bullets, and that Loughner had another magazine that held about 30 bullets, as well as two others that each held about 15 bullets.
Reese Widmier, manager of the Sportsman's Warehouse in Tucson, confirmed to the Post that the gun was sold by the store Nov. 30.
Loughner did pass the federally required background check, Widmier told the newspaper.
Dr. Park Dietz, a forensics psychiatrist, told AOL News today that gun control laws make it difficult to determine whether someone is mentally stable enough to purchase a gun.
"He's old enough to buy it on his own because there was no way to determine this was a mentally ill person," Dietz said. "The only thing the existing law does about that is quite absurd. The ATF form asks if you have ever been adjudicated mentally ill," he said in reference to the federal Bureau of Alcohol Tobacco and Firearms.
Dietz noted that he once had law students visit 25 people on a ward for the criminally insane who had been adjudicated dangerously mentally ill, asking them whether they had been adjudicated dangerously mentally ill.
"They all said no, while sitting on the ward," Dietz told AOL News.
"In some states the instant background check does include a search of computer records of who has been committed as dangerously mentally ill but it is quite inconsistent around the country whether they do it or how complete the information is."
Arizona does not have a waiting period unless something is flagged during the instant check.
However, the debate in Arizona is far from simple. Giffords herself is a long-time gun owner who has described herself as a strong supporter of the Second Amendment. And despite the lack of restrictions on gun purchases and ownership in Arizona, not everyone agrees that the laws should be toughened.
Sen. Rand Paul, R-Ky., said on "Fox News Sunday" today that the shootings are "unrelated" to Arizona's gun laws: "The weapons don't kill people, it's the individual that kills people."
On NBC's "Meet the Press," Rep. Raul Labrador also said changes in gun laws are not the answer, but the answer lies with each individual who owns a gun.
"I don't know if it's the gun laws that make a difference," the Idaho Republican said.
However, Arizona's Democratic Rep. Raul Grijalva, on the same program, said: "Gun laws have to be examined."
"This is clearly an illustration of why we must all work together to fight gun violence in America and keep dangerous weapons out of the hands of the wrong people," she said in a statement.
Giffords' Republican challenger to office during the last election, Jesse Kelly, who was pictured on his campaign website in military gear, holding his automatic weapon, did not blame gun laws or political rhetoric for the rampage.
"Arizona is a state where people are firearms owners," he told The Associated Press after Saturday's shooting. "This was just a deranged individual."