Tonight's show didn't have as many headlines on the screens like we usually see, but there was still a lot of material referenced. The citations after the jump include the Ezra Klein piece Rachel discussed at length and the two shooter profile studies David Cullen mentioned in the opening block.
Timeline: Deadliest U.S. mass shootings
Don't Jump to Conclusions About the Killer By DAVE CULLEN
National Threat Assessment Center - Secret Service Safe School Initiative
FBI report: The School Shooter: A THREAT ASSESSMENT PERSPECTIVE (pdf)
Obama wants 'meaningful action' in the wake of Conn. Massacre
Police search for motive after 5 killed at Norcross spa
3 students killed, several hurt in shooting at Chardon High School; suspect in custody
Gunman Kills 7 in a Rampage at a Northern California University
3 dead, 2 wounded in Tulsa shooting spree
Seattle Cafe Shooter Kills 5, and Himself After Citywide Manhunt
Dark Knight Rises Shooting LIVE: Masked Gunman Kills 12 in Batman Rampage
6 dead, including gunman, in Minn. workplace shooting
Gunman Kills 6 at a Sikh Temple Near Milwaukee
Three Killed in Shooting at Spa in Wisconsin
Shooting rampage at Clackamas mall leaves 3 dead, including shooter
More Guns, More Mass Shootings—Coincidence?
Why are mass shootings becoming more common?
Twelve facts about guns and mass shootings in the United States
Jacob Tyler Roberts Identified As Clackamas Town Center Shooter
Mythbusting: Israel and Switzerland are not gun-toting utopias
Statements of Mayors Against Illegal Guns Co-Chairs on Newtown, Connecticut Shooting
NRA Members Agree: More Gun Regulation Makes Sense
Letter from the President -- War Powers Resolution
Panetta Orders Deployment of U.S. Antimissile Units in Turkey