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The number of death sentences handed down in the US dropped by a third in 2015, continuing a long-term trend, but one county in California seems to be going against the grain. It handed down 16% of all death sentences in the country despite being home to less than 1% of the population. Why?

Only six US states carried out executions this year - Texas, Missouri, Georgia, Florida, Oklahoma and Virginia.

California, which last executed a convict on death row in 2006, was not among them.

However, California topped the list of states handing down death sentences, contributing 14 to the nationwide total of 49.

And eight of those death sentences came from one county alone - Riverside, which is situated to the east of Los Angeles and stretches all the way to the border with Arizona.

This is despite the fact that Riverside has a population of only 2.3 million, compared with 39 million in California as a whole.

So why is Riverside so keen on the death penalty?

A glance at statistics from previous years suggests that eight death sentences in one year is quite high for Riverside. In 2014 there were three, in 2013 there were six.

But this is still high by the standards of California and the US as a whole. Riverside's western neighbour, Los Angeles County, with a population more than four times as large, handed down three death sentences in 2015. From 2012 to 2014 inclusive Los Angeles County issued 17 death sentences but Riverside was not far behind, with 13.

Death sentences Year Los Angeles County Riverside County 2015 3 8 2014 4 3 2013 7 6 2012 6 4 Source: Death Penalty Information Center

Judged by the number of death sentences handed down, Riverside has ranked no lower than third among the US's more than 3,000 counties since 2012, and was first in 2015.

"The county is the most glaring example of a phenomenon that is being seen across the US, which is that even though the death penalty is in broad decline across most of America, there are individual pockets that continue to disproportionately use it," says Robert Dunham, executive director of the Death Penalty Information Center.

He cites a 2013 report done by the centre which found that the majority of people on death row in the US were sentenced to death by fewer than 2% of the counties.

California had 746 people on death row in January 2015, far ahead of the state in second place - Florida, with 400.

University of California Berkeley law professor Franklin Zimring says there are plenty of reasons why Riverside may be responsible for so many death sentences.

For one thing it has a "somewhat tougher and more conservative political reputation than [California's] coastal counties", he says.

However, he says the key determining factor for a county handing down lots of death sentences is the district attorney.

"You don't have death sentences without a capital trial, and the district attorney is the one that ultimately decides how many capital trials are going to happen - and some seem to go after them more aggressively than others," he says.

Riverside County District Attorney Mike Hestrin says the people of Riverside support the death sentence to greater degree than other counties and "there is a certain feeling of how they want criminal justice to operate".

But he says death sentences are only imposed when it's necessary to achieve justice.

"We had eight cases this year and the juries and judge agreed," he says.

When he took over as DA in January he reviewed each of the 22 pending death-penalty cases, he says, and decided to stop seeking death in six of them.

"That's a 30% reduction from my predecessor. Of the 11 new cases that came in this year, where I was the first to make a determination, I am only seeking the death penalty four times," he says.

Hestrin is part of a group of district attorneys, law enforcement and victims' rights advocates who are pushing for a 2016 ballot initiative that could speed up the death penalty process by accelerating appeals, among other things, in California.

The system is "terribly broken," he argues, with people sentenced to death having to wait up to seven years for an appeals lawyer.

Zimring agrees that the system needs reform, saying a capital trial is just the start of a "hugely expensive" process and a "marathon of legal procedure".

But he is optimistic about the direction of travel for anti-death-penalty campaigners.

"In 1995 the same number of death sentences in Riverside would have accounted for 3% or 4% of American death sentences, not 16%," he says.

"Plus the fact that LA, which tends to be the centre of gravity for capital prosecutions due to the size and nature of the population and violent crime, isn't in first place suggests more realistic policy decisions are coming from the LA county office, which is by no means a hotbed of liberal sentiment.

"That for me is more statistically significant than Riverside."

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