It Appears That Arizona Shooter’s Odd Behavior Caused Growing Alarm Prior To Massacre
Mr. McGahee, for one, was disturbed enough by the experience to complain to school authorities, who as early as last June were apparently concerned enough themselves to have a campus officer visit the classroom. And what Mr. McGahee described as a pattern of behavior by Mr. Loughner, marked by hysterical laughter, bizarre non sequiturs and aggressive outbursts, only continued. ...
“I was getting concerned about the safety of the students and the school,” said Mr. McGahee, who took to glancing out of the corner of his eye when he was writing on the board for fear that Mr. Loughner might do something. “I was afraid he was going to pull out a weapon.”
A student in the class, Lynda Sorenson, 52, wrote an e-mail to a friend expressing her concerns.
“We do have one student in the class who was disruptive today, I’m not certain yet if he was on drugs (as one person surmised) or disturbed. He scares me a bit,” Ms. Sorenson wrote in an e-mail in June that was forwarded Sunday to The New York Times. “The teacher tried to throw him out and he refused to go, so I talked to the teacher afterward. Hopefully he will be out of class very soon, and not come back with an automatic weapon.”
Mr. Loughner’s behavior grew so troubling that he was told he could no longer attend the school, and he appeared, given his various Internet postings, to find a sense of community in some of the more paranoid corners of the Internet. ...
http://www.nytimes.com/2011/01/10/us/10sho...

My question is: why was this nutcase allowed to legally purchase a semi-automatic pistol?