Media playback is unsupported on your device Media caption Bernard Parks: "It was the singular most important piece of evidence"

The Los Angeles riots erupted on 29 April 1992 after four white police officers were acquitted over the videotaped beating of black motorist Rodney King.

Anger led to days of looting and burning, 54 deaths and $1bn (£610m) of damage to the city. A state of emergency was declared in South Central Los Angeles.

In the wake of the riots the Los Angeles Police Department (LAPD) was forced to change.

The grainy black and white footage of King's beating offered proof of what the black community had been complaining about for decades - police brutality.

Some LAPD officers reporting on disturbances in the black communities of South Los Angeles in 1992 used code to describe disturbances in their areas: NHI - "No Humans Involved".

Members of the predominantly white, male police force said it was "gallows humour" and regularly described the African-Americans they were meant to protect and serve as "monkeys" and "gorillas".

An independent commission to investigate the King beating detailed a culture of racism and abuse within the LAPD, where excessive force was not only tolerated but often covered up by fellow officers in a code of silence.

"With the Rodney King beating and the riots, that was the beginning of the end of the old imperial LAPD. Because LAPD had a very arrogant, 'we're above the law' attitude," says Connie Rice, a civil rights lawyer.

Image caption Shopping centres an cars were set alight during the riots

"It was the first time the black community's complaints couldn't be denied and swept under the rug."

The commission, led by future US Secretary of State Warren Christopher, depicted an out of control LAPD with rogue officers beating suspects and bragging about it over patrol cars' communication systems.

The report published the messages to illustrate the King beating was not an isolated incident. It noted that LAPD management monitored the messages but did nothing about the abuse.

Some memorable messages include:

"I hope there is enough units to set up a pow-wow around the susp so he can get a good spanking and nobody see it."

"I obviously didn't beat this guy enough. He got right back up and is still being obnoxious."

"The last load went to a family of illegals living in the brush along side the pas frwy [Pasadena Freeway]… I thought the woman was going to cry … so I hit her with my baton."

Caught on camera

While the use of excessive force was not uncommon, what made the Rodney King beating unusual is that it was captured on camera.

Where is Rodney King now? Twenty years after he became a symbol of the riots, Rodney King says he is at peace. He has written a book, The Riot Within: My Journey From Rebellion to Redemption. He has been enjoying a book tour with his fiance Cynthia, aka 'Juror Number Five' from his civil trial, which ordered the city of Los Angeles to pay him $3.8m. King says the book helped him recover. "In that first Simi Valley trial, when I went to Simi Valley I never got on the stand to testify. This is like my chance to testify," King told the BBC, referring to his trial which was held outside Los Angeles in a predominantly white area. "I didn't feel like I was a part of that first trial so it was good for me to write this." King, who during the height of the riots implored people to stop fighting and "get along," said he feels like he has played a small part in the civil rights movement and the change within the LAPD. "Things have changed. They've been working on it ever since. The whole force had to look at themselves. They still have some work in there to do, some things to be weeded out, but they changed. Change is good."

The footage - and the ensuing outrage - forced the LAPD to change radically. But change did not come overnight.

When the Christopher Commission released its report and recommended ways to reduce racism, sexism and the use of excessive force, some officers reportedly held a bonfire party to show what they thought of the findings.

The LAPD was about 68% white in 1992. When the riots broke out, Bernard Parks, now an LA city councillor, was LAPD Deputy Chief - the highest ranking African-American officer on the force at the time.

"The big battle inside of LAPD was people trying to determine where they came out on the side of whether it was appropriate or inappropriate using force on Rodney King. There was a lot of tension around that," says Mr Parks.

"There were those who thought, 'Hey, what happened to Rodney King, he deserved it, he was running from the police. If he hadn't have done that the police wouldn't have done what they did.'

"And there were others, like myself, who said, this is inappropriate. No matter what happened before the camera came on, it couldn't justify what you saw on the tape."

Mr Parks, who became chief of police in 1997, says the video led to changes within the LAPD and that the community's complaints were ultimately taken more seriously.

Image caption Rodney King signed this image from the video of his arrest during a book-signing in Los Angeles

Many of the Christopher Commission recommendations focused on boosting multiculturalism in the police force, so that the officers would better reflect the communities they patrol. The force has slowly shifted from a paramilitary style to more interactive, community policing.

Officers who were once appraised by the number of the arrests they made are now encouraged to prevent trouble before it happens, says Connie Rice, who has moved from "constantly suing" the LAPD to working with them.

"I've even got a parking space there," laughs Ms Rice, who has been working with the LAPD on a programme placing 50 police officers in four housing projects.

"Their job is to help communities become healthy so crime plummets in those housing projects. These cops will get promoted for demonstrating how they avoid arresting a kid."

Changing South Central

While Rodney King may have been the catalyst that sparked the Los Angeles riots, the conditions in South Los Angeles are arguably what caused them.

The area was dominated by gangs and a lack of education, jobs and opportunity. Crack cocaine use was rife and young people often found joining gangs like the Bloods or Crips their safest bet for a future.

The neighbourhood has changed a lot in 20 years.

The crime rate is down. And the area is now called South Los Angeles and proudly boasts neighbourhood names, rejecting the toxic "South Central" and all its connotations of ghettos and violence.

The population is now mostly Hispanic, not African-American.

But much is still the same. South LA is still poor and struggling with gangs and a lack of opportunity.

While much inside and out of the LAPD has improved, Mr Parks says it is naive to think riots could not happen again, especially when there is such a chasm between the rich and poor in the city.

People who say they predicted the riots are kidding themselves, he said.