From this story on Comcast.net:
With few new details emerging at Monday's hearing, questions remained about what could have motivated someone to arm himself with a pistol and magazines carrying 33 bullets each, and rain gunfire on a supermarket parking lot crowded with men, women and children. 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. The official did not know what type of drug was detected.
_Prosecutors say he scrawled on an envelope the words "my assassination" and "Giffords" sometime before he took a cab to the shopping center. Police said he bought the Glock pistol used in the attack at Sportsman's Warehouse in Tucson in November. The revelation about the shooter's high-capacity magazines led one longtime Senate gun control advocate, Sen. Frank Lautenberg, D-N.J., to announce plans to re-establish a prohibition that lapsed in 2004 on magazines that feed more than 10 rounds at a time.