The killings were brutal and carried out in cold blood but who was behind them?
Monica Quan, 28, a college basketball coach, and her partner Keith Lawrence, 27, were found murdered in their car outside their home in February 2013.
The pair had recently announced their engagement. Shortly afterwards, two police officers were ambushed while they waited at a red light.
Michael Crain, one of the officers, was killed. The 34-year-old was a father of two. His partner was left critically injured.
A manifesto appeared online, written by the gunman. He was Christopher Dorner – a former Los Angeles Police Department officer.
He talked of an unfair dismissal, racism, corruption and named individuals in his writings.
Two officers were assigned to protect one of the named individuals, but they were fired upon, leaving one injured.
A huge manhunt ensued, which would leave not only Christopher Dorner dead, but another officer too, bringing the body count to four.
But what turned this former officer from cop to killer?
Christopher was born in New York State and moved to California with his mother, Nancy, and sisters soon afterwards.
It’s said that he experienced racism in his school years. Yet he had a keen interest in public service and as a teen, he signed up with the local police department youth programme in the hope of eventually becoming a fully fledged officer.
From 1997 to 2001, Christopher attended university and he received a Bachelor’s degree in political science.
He played on the American football team while he was there. A fellow student and sportsman later said of Christopher: ‘The person I knew was this smart, good man. He was honest and thoughtful, he had integrity – he was a really likeable guy.’
It was a year after graduating that he joined the US Navy – a vocation that Christopher seemed to excel in.
By 2006 he’d achieved the rank of lieutenant, and during his service he was awarded various medals and commendations including Global War on Terrorism Service Medal, Rifle Marksman Ribbon, Pistol Expert Medal and the National Defence Service Medal.
Accustomed to military structure, Christopher would often insist on following protocol at all times.
He then applied to join the Los Angeles Police Department whilst remaining in the Naval Reserve. It was there that his unblemished record changed.
Christopher was accused of punching another recruit – an accusation he strongly denied.
He was reportedly suspended for accidentally discharging a gun and was thought to clash with authority frequently.
‘His personality process, in my opinion, did not fit with law enforcement,’ Ron Martinelli, a former police officer, said. ‘You can’t seek to control others unless you are in control of yourself. I’m very surprised he was even selected to be a police officer.’
Christopher Dorner said he suffered racial abuse from two other officers and that they merely received a 22-day suspension. He also made a formal complaint about his field-training officer, saying that he’d kicked a mentally ill suspect in the head during an arrest.
An investigation was launched and a disciplinary hearing followed in 2008. Yet that hearing found that Christopher lied about what he’d witnessed and the LAPD fired him.
A friend later said this would have come as a huge psychological blow to Christopher who prided himself on his integrity.
‘I don’t think this had as much to do with his career so much as his being called a liar. You could call him whatever you want, just don’t call him a liar,’ the friend said.
Christopher Dorner tried in vain to have his dismissal overturned, but in 2010 a judge upheld the LAPD’s decision.
It likely fed his long-festering anger at a society he thought of as racist and brutal.He became more isolated, stopped having contact with friends, and his relationship with his sisters and mother broke down too.
An ex-girlfriend of Christopher’s also posted a warning on a website called dontdatehimgirl.com after they split, saying women should steer clear of him because of ‘the fluctuation of his behaviour, the swinging from the highs to the lows.’
And in February 2013, he shot and killed Keith Lawrence and Monica Quan. Monica’s father, Randall Quan, was a former captain in the police force and had represented Christopher at the disciplinary hearing in 2008.
Christopher thought that he’d done an inadequate job…‘I never had the opportunity to have a family of my own,’ Christopher Dorner wrote in his 6,000-word manifesto. ‘I’m terminating yours.’
And the killings didn’t stop there…He injured another police officer, gunned down Michael Crain and a six-day manhunt ensued. Law enforcement agencies worked together and a reward was offered in the hope of catching Dorner.
Eventually, he was cornered inside a mountain cabin in Big Bear.
Dorner shot at the police, killing one deputy – Jeremiah MacKay – and wounding another.
Tear gas and pyrotechnic canisters, which generate high temperatures, were thrown into the cabin in a bid to flush him out. The cabin caught fire and Dorner, 33, shot himself in the head. His charred remains were later identified.
The former upstanding citizen was dead – but he’d needlessly taken the lives of four innocent people before his own.