Kenyon Marc Youngstrom, a 37-year-old California Highway Patrol officer and U.S. Army veteran, was shot while on duty on September 4, 2012, and died of his wounds the next day. He was patrolling southbound I-680 near Livorna Road in Alamo, California, when he and fellow officer Tyler Carlton stopped a Jeep for an obstructed license plate. As Youngstrom approached the vehicle the driver produced a handgun and shot him in the head. Officer Carlton returned fire, fatally wounding the shooter.

The shooter was identified as 36-year-old Christopher Boone Lacy. Investigators reported Lacy had a history of bipolar disorder and prior mental health crises, had become increasingly reclusive in the year before the shooting, and had posted interest in libertarian and Sovereign Citizen ideas. The handgun had been legally purchased in 2010. Youngstrom, who had served seven years with the CHP, is survived by his wife Karen, their four children, his parents, and several siblings.

What details about that traffic stop or about Lacy’s recent behavior might help explain how an encounter escalated to this level?