CALIFORNIA (REUTERS) - "I always hope, I always had hope."

71-year-old Craig Coley spent more than half his life behind bars for a double murder he did not commit.

He will now spend the rest of his life as a multi-millionaire.

Mr Coley has just reached a US$21 million (S$28.4 million) settlement with the city of Simi Valley after spending 39 years in prison.

Mr Coley was wrongfully convicted for killing his former girlfriend Rhonda Wicht and her four-year-old son Donald in their apartment in 1978.

"From day one, I told them do what you want to do to me, but keep looking, don't stop, you have the wrong man," said Mr Coley.

Mr Coley had always maintained his innocence and was pardoned in 2017 by California's then-governor Jerry Brown based on lost DNA evidence found at the scene.

"People need to realise that these things occur out there, police are human, they make mistakes," he added.

A home video shot when Mr Coley was released shows him being hugged by former Simi Valley detective Michael Bender, who helped prove his innocence.

The retired officer quit his job in 1991. He was convinced Mr Coley was innocent.

"Any legal charge against anybody is a search for the truth, period, nothing else," said Mr Coley.

Last year, California authorities awarded Mr Coley US$1.95 million - that's US$140 for each day he spent in prison.

At the time, it was the largest payout for a wrongful conviction by the state's Victim Compensation Board.

Officials say the 39 years Mr Coley spent behind bars is the longest prison term ever overturned in California.