The suspect in Rep. Gabrielle Giffords' shooting wrote the words "Die, bitch" on a note found in his home, a sheriff's official said Tuesday.
Pima County Chief Rick Kastigar told The Associated Press that authorities believe the note was a reference to Giffords. It was found alongside other menacing notes including "I planned ahead," "My assassination" and the name "Giffords."
Authorities are learning other new information about the events leading up to the assassination attempt.
Sheriff Clarence Dupnik told the AP that on the morning of the shooting, Jared Loughner's father saw his son take a black bag out of a car trunk.
The sheriff said the father approached Loughner, and he mumbled something and took off running. The father got in his truck and chased his son into the desert as he fled on foot.
Loughner took a taxi cab to the supermarket where the three-term Democrat was holding a meeting to hear the concerns of her constituents.
The revelations came on the same day investigators told NBC News that shell casings recovered at the scene of Saturday's mass shooting confirmed the Glock-wielding gunman fired 31 times using the semiautomatic pistol.
And Bloomberg News reported that pistol sales soared in Arizona on Monday. Citing FBI data, Bloomberg said one-day sales of handguns in Arizona for Jan. 10 were 263 — 60 percent higher than on the corresponding Monday a year ago.
Six people were killed, including U.S. District Judge John Roll and 9-year-old Christina Taylor Green. Giffords and 12 other people were shot during the rampage outside a Safeway supermarket.
Loughner, 22, is charged with one count of attempted assassination of a member of Congress, two counts of killing an employee of the federal government and two counts of attempting to kill a federal employee.
Loughner had trouble with the law, was rejected by the Army after admitting to drug use and was considered so mentally unstable that he was banned from his college campus, where officials considered him a threat to other students and faculty.
But Loughner had no trouble buying the Glock semiautomatic pistol that authorities say he used in the rampage.
Loughner's personal history did not disqualify him under federal rules, and Arizona doesn't regulate gun sales. His criminal charges were ultimately dismissed, the Army information was private and Pima Community College isn't saying whether it shared its concerns about Loughner with anyone besides his parents.
Loughner cleared a federal background check and bought the pistol at a big-box sports store near his home on Nov. 30 — two months after he was suspended by the college. He customized the weapon with an extended ammunition clip that would have been illegal six years earlier.
Investigators told NBC News that Loughner had a 30-round magazine on his Glock-19, plus one round in the chamber, for a total of 31 rounds in the weapon. Of the 31 rounds, a least 20 struck those outside the Tucson supermarket. Some victims were struck by more than one round.
It was not clear whether Loughner was able to put the second magazine into the Glock, investigators said. An examination of the second magazine showed that its spring was defective, so it would not have functioned properly, NBC News reported.
Witnesses said they grabbed the magazine as Loughner tried to load the gun.
“The reason he was able to be tackled was he had to pause to reload,” Dennis Henigan, vice president of the Brady Center to Prevent Gun Violence, told The New York Times. “The problem is, he didn’t have to pause to reload until he’d already expended 30 rounds.”
Loughner purchased a Glock from a Sportsman's Warehouse in November. He reportedly bought his ammunition at a Walmart store just hours before the shooting. He tried to buy ammunition from one Walmart, but left before completing the transaction, according to the company. He then reportedly purchased bullets from a nearby Walmart.
Glock owners, sales
Outside Sportsman's Warehouse, the cavernous store where Loughner purchased his Glock, gun owner Jason Moats said that "the bad guys can get the guns either way." He suggested that the shootings could have been less tragic had there been one more weapon out there, rather than one less.
Glock pistol sales surged in the aftermath of the shootings, Bloomberg reported on Tuesday.
Karen Seaman, chief marketing officer for Sportsman's Warehouse, said Loughner passed a federal background check required to buy a gun.
According to online FBI data, the government conducted about 124 million background checks between Nov. 30, 1998 and Dec. 31, 2010. Of those, 821,000 — a fraction of 1 percent — were rejected.
Background checks are designed in part to weed out prospective gun buyers who have felony criminal records, have a history of domestic violence or are in the country illegally. None of that applied to Loughner, although the background check form asks about drug use and friends say he frequently used marijuana in high school.
In October 2007, Loughner was cited in Pima County for possession of drug paraphernalia, which was dismissed after he completed a diversion program, according to online records.
Loughner was arrested in October 2008 on a vandalism charge near Tucson after admitting that he vandalized a road sign with a magic marker, scrawling the letters "C" and "X" in what he said was a reference to Christianity. The police report said Loughner admitted other acts of vandalism in the area. The case was ultimately dismissed after he completed a diversion program.
A military official in Washington said the Army rejected Loughner in 2008 because he failed a drug test. The official spoke on condition of anonymity because privacy laws prevent the military from disclosing such information about an individual's application.
Last year, Pima Community College police were called in five times to deal with Loughner's classroom and library disruptions. He was suspended from the college in September after campus police discovered a YouTube video in which Loughner claimed the college was illegal according to the U.S. Constitution. School officials told Loughner and his parents that to return to classes he would need to undergo a mental health exam to show he was not a danger.
A college spokesman did not respond to an e-mail asking if the college had referred any information on Loughner to local police.
On Nov. 30, the same day he bought the Glock, Loughner posted a YouTube video that raged against the college and police.
"If the police remove you from the educational facility for talking then removing you from the educational facility for talking is unconstitutional," he wrote on the video. "The situation is fraud because the police are unconstitutional. ... Every Pima Community College class is always a scam!"
Federal law bars gun ownership for people who've been judged dangerously mentally ill by a court and those who have been committed to a mental institution, thresholds that didn't disqualify Loughner. Less than 1 percent of the federal government's background-check rejections involved mental-health issues, according to the records.
"It's not easy to draw that line" of when a person's mental illness should disqualify them from owning a weapon, said Michael J. Fitzpatrick, executive director of the National Alliance on Mental Illness, an advocacy group.
"The reality is most people with mental illness are not violent," he said. "The issue, frankly, is getting people into treatment. It's not about guns."
In other developments Tuesday:
- A surveillance video recorded some of the shooting scene, which law enforcement officials say showed Loughner coming in and out of the picture, NBC News reported. A second man seen entering the Safeway store with Loughner turned out to be a cab driver.
- At University Medical Center, Giffords remained in critical condition, but doctors said she is able to breathe on her own.
- Parents of one of Loughner's close friends, Zach Osler, described a troubled relationship between the suspect — an only child — and his parents.
- Members of the judiciary branch mourned the loss of one of their own with the death of Roll.
- U.S. District Judge Raner Collins in Tuscon ruled that federal judges assigned to Arizona's Tuscon Division were barred from presiding over the prosecution of Loughner to avoid appearance of impropriety.
- The Arizona Legislature sent to Gov. Jan Brewer a bill banning protests at or near funeral sites. The action came after the Westboro Baptist Church of Kansas said it would picket the funeral of 9-year-old Christina Green because "God sent the shooter to deal with idolatrous America."
NBC News correspondent Pete Williams, msnbc.com staff and The Associated Press contributed to this report.