San Francisco Chronicle, January 16, 2009 by Tyche Hendricks
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/01/16/BAP5159KH0.DTL&type=printable
“The vast majority of victims and perpetrators have past involvement in the criminal justice system,” said David Onek, director of the Berkeley Center for Criminal Justice … who recently completed a study on San Francisco homicides. “Violence in San Francisco is highly concentrated in a small number of places and a small number of people.”