Editor's note, Dec. 14: This story on the prevalence of previously identified mental health problems among mass shooters has new relevance in light of the Newtown tragedy.

Mass murderer Jared Loughner was sentenced on November 8 to multiple life terms in prison. It's difficult to read an account of the court proceedings in Tucson without getting a lump in your throat. The man who shot 19 people at a shopping center in January 2011—gravely wounding former US congresswoman Gabby Giffords, and killing six including a federal judge and a 9-year-old girl—faced potent testimony from some of his victims.

"You may have put a bullet through her head, but you haven’t put a dent in her spirit and her commitment to make the world a better place," said Giffords' husband, Mark Kelly, as his still-recovering wife gazed directly at Loughner from her seat across the courtroom.