Pittsburgh Post-Gazette, April 13, 2009 by Mark Roth
http://www.post-gazette.com/pg/09103/962453-53.stm
An incident March 21 in which a man killed four Oakland, Calif., police officers and then was shot to death himself also does not fit the usual mass killing pattern, Dr. Zimring said. The suspect in that case was facing a return to prison when he was pulled over at a traffic stop and probably shot the first officer in a state of panic, “and all the other killings followed from that first one.”