This Aug. 20, 2014 file photo several hundred demonstrators march through Oakland, Calif. protesting the police shooting of unarmed black 18-year old Michael Brown in Ferguson, Mo. The San Francisco Bay Area's three largest police unions publish an "open letter" saying recent the anti-police rhetoric demonstrations have reached dangerous levels.
This Aug. 20, 2014 file photo several hundred demonstrators march through Oakland, Calif. protesting the police shooting of unarmed black 18-year old Michael Brown in Ferguson, Mo. The San Francisco Bay Area's three largest police unions publish an "open letter" saying recent the anti-police rhetoric demonstrations have reached dangerous levels. Noah Berger AP
This Aug. 20, 2014 file photo several hundred demonstrators march through Oakland, Calif. protesting the police shooting of unarmed black 18-year old Michael Brown in Ferguson, Mo. The San Francisco Bay Area's three largest police unions publish an "open letter" saying recent the anti-police rhetoric demonstrations have reached dangerous levels. Noah Berger AP