The Oakland police department (OPD) has long been one of the most controversial urban law enforcement agencies in America, with a string of high-profile criminal and brutality allegations going back decades.

It is also tough turf to police. Oakland is a city that has suffered from considerable urban blight, gang problems and drug issues. It is a historic centre of black American culture and radical black politics, having given birth to the Black Panther movement in the 1960s. There have been persistent reports of police criminality and abuse, especially aimed at the city's black population, where community activists say low-level police harassment is a fact of life. Latest census figures show black people make up the biggest single ethnic group in Oakland at 27.3%, with white people at 25.9% and Hispanics at 25.4%.

Despite having almost the same size populations in the city, however, white people account for only 16% of OPD vehicle stops, and 6.7% of motorists searched. Black people in Oakland, by contrast, account for a whopping 48% of vehicle stops, and 65.8% of motorists searched.

But it is the major incidents that really stand out when examining how OPD polices its community, and in particular the poorer black neighbourhoods of Oakland. In 1968 OPD officers shot and killed Bobby Hutton. The 17-year-old Black Panther party member was involved in a shootout with police, but surrendered and stripped down to his underwear to show he was unarmed. However, he died after being shot by police at least 12 times.

That incident helped set a tone of discord between OPD and large segments of the city's black community that has lasted until the present day. Community activists say too many OPD officers live outside the city and commute, thus separating themselves from Oakland's daily life. That feeling was notoriously reinforced by the emergence of a gang of rogue police officers in the 1990s dubbed the "Rough Riders".

They were accused of planting evidence, beating up suspects and falsifying police reports to frame their victims. Their actions eventually resulted in a class action lawsuit against the city, and Oakland ended up paying out millions of dollars in compensation to at least 119 plaintiffs.

Scores of drug cases were dropped because of tainted evidence. However, after the officers were fired from the OPD, a jury that had no black members on it ended up clearing the four Rough Riders on eight of the counts against them, and were unable to reach a decision on 27 others.

After the Rough Riders trial, the OPD was placed under the external oversight of a district judge. However, an investigation by the Investigative Fund of the Nation Institute and the Investigative Reporting Program at UC Berkeley recently showed that the OPD has continued to have a disturbing record of violence – and has closed ranks to cover it up. The report revealed that a 2003 court case on access to police records, which ended in a 2006 supreme court decision called the Copley ruling, has been used by OPD to prevent details of complaints about police becoming public knowledge.

The ruling undermined the longstanding position of Oakland's Citizens Police Review Board, which civil rights groups had effectively campaigned to set up as a way of holding the OPD accountable. After the Copley ruling, complaints packets about allegations of abuse by OPD officers were no longer available to the public. The investigation also discovered that just 16 officers were responsible for almost half of the police shootings in the city between 2000 and 2010 (40 of 85 shooting episodes), reinforcing the idea that a core of rogue OPD officers still exist in the force.

Nor has external judicial oversight of OPD prevented further headline-catching controversies from assailing the force. Oakland journalist Chauncey Bailey was shot dead in the city's downtown in 2007 while investigating the activities of a local black Muslim group.

However, after a bungled and controversial OPD investigation into the case, a Department of Justice report castigated local police for their incompetent work on Bailey's death. The report slammed OPD officer Derwin Longmire for failing to adequately investigate suspect Yusuf Bey, with whom Longmire appeared to have a close personal relationship.

It detailed numerous incidents of Longmire failing to do basic investigations on Bey and allowing him special privileges while in police custody, such as using his phone. The report only became public two years after it was written because Oakland city and police officials refused to release it.

Then on 21 March 2009, Oakland was riven by violence after two police officers were shot dead by Lovelle Mixon during a traffic stop. The resulting manhunt for Mixon, which resulted in his death, also saw two more police officers shot and killed as hundreds of OPD officers descended on the neighbourhood where Mixon was hiding, apparently with little co-ordination or order.

A report into the day's events again excoriated OPD tactics and a failure to follow established police procedures, especially when officers stormed the apartment where Mixon was hiding without adequate back-up, using flash-bang grenades that set it on fire and when there was no hostage situation.

A final incident to grip the city recently involved not the OPD itself but a police officer from Bay Area Rapid Transit (Bart). At a subway stop in Oakland, Oscar Grant, a young black man, was arrested in 2009 by Bart police investigating a fight. Despite being handcuffed and lying on his stomach on the floor, Bart officer Johannes Mehserle pulled out his gun and killed Grant with a single shot in the back. Mehserle claimed he thought his weapon was his Taser.

The news sparked serious unrest in the city after outraged protesters demonstrated against the shooting. Mehserle was found guilty of manslaughter and got two years. He was released on parole in June 2011. The incident was widely recorded on video.