Gunman Jared Loughner was a Brain Damaged Pot User,

"Sometimes religion was brought up or drugs. He smoked pot..." (The Houston Chronicle)

"He was a pot head and into rock, like Hendrix, The Doors, Anti-Flag..." (KTLA-TV)


The Science:

Cannabis and adolescence: A dangerous cocktail (McGill University Health Centre)

Cannabis Triggers Transient Schizophrenia-like Symptoms (Yale School of Medicine)

Early cannabis users three times more likely to have psychotic symptoms (University of Queensland, Australia)

Scans reveal brain damage from cannabis is like schizophrenia (Albert Einstein College of Medicine)


Sources:
AP on AZ Suspect: 'Former Classmate Described Loughner As a Pot-Smoking Loner Who Had Rambling Beliefs About the World' (CNSNews)
Did Pot Trigger Giffords Shooting? (David Frum)

This just goes to show how much of a waste of life pot users are, they are not only some of the dumbest people on the planet they are dangerous.

Loughner Pot Report (The Smoking Gun)