Why won't Barack Obama prosecute CIA torturers?

The graphic and unsparing report released this week on the CIA's use of torture has prompted widespread calls for criminal charges to be brought against American spies involved in the agency's detention programme.

But while the White House has said it condemns the use of so-called "enhanced interrogation techniques" it is steadfastly refusing to prosecute those who ordered the torture or carried it out.

Here's what you need to know about this charged issue:

Torture is illegal under US law

American law specifically prohibits the use of torture, which it defines as person acting under the guise of legal authority "to inflict severe physical or mental pain or suffering" on someone under their physical control.

Mental suffering includes threatening someone with imminent death or doing something to "disrupt profoundly the senses or personality".

The law isn't limited to US territory - an American citizen can be prosecuted if they torture anywhere in the world.

So a CIA officer keeping a prisoner awake for a week until they start to hallucinate would seem to fit the definition of torture.

So would threatening them with a drill, or handcuffing them above their heads for 22 hours at a time, or waterboarding them until they convulse and vomit. All of these things were done at secret CIA prisons around the world.

But the Obama administration has said it isn't going to prosecute anyone

Shortly after President Barack Obama took office in 2009, his attorney general said the new administration "would not prosecute anyone who acted in good faith and within the scope of the legal guidance" given to the CIA by Bush administration lawyers.

Federal prosecutors investigated for three years before deciding in 2012 not to bring any charges. This week the Justice Department said there was nothing in the newly-released torture report that would cause them to revisit the decision not to prosecute.

Their reasons for not prosecuting are partly legal...

There are rows of hurdles standing in the way of a prosecution. Securing a conviction in cases where details are murky and sometimes classified is going to be difficult. Juries are also considered pretty unlikely to convict a CIA agent who deployed to a dangerous place and says they were only following orders and trying to keep America safe in the wake of the September 11 attacks.

...but there is a lot of politics involved

The release of the report has been explosive. Deep rifts between the CIA and the Democratic Party have erupted into public view. Morale has slumped at the spy agency and Republicans are accusing the White House of leaving America's spooks to swing in the wind.

Imagine how much worse all of that would be if the Obama administration was actually trying to send people to prison. The President would be prosecuting the friends and colleagues of the spies he relies on every day to keep the US safe from terrorism. If the Justice Department went after George W Bush or Dick Cheney or other senior officials it would be seen as using the criminal justice system to persecute political opponents.

Mr Obama and his aides may also fear that if they initiate prosecutions for torture they may one day face charges themselves over America's deeply-divisive campaign of drone strikes.

There are some alternatives to prosecuting

Prosecutions are partly about punishing people who break the law. But they are also about bringing the facts of their crimes to light and registering society's deep disapproval for what they did.

Punishments seem to be off the table but there are ways to achieve the second part of that goal. The US could have a sort of truth and reconciliation commission, like the one set up in South Africa after apartheid, where torturers and the tortured could both explain themselves without fear of reprisal.

An interesting suggestion by the American Civil Liberties Union, a civil rights group: Mr Obama should issue pardons to Bush, Cheney and the CIA officers as a way of registering that what they did was illegal without actually charging.

"An explicit pardon would lay down a marker, signaling to those considering torture in the future that they could be prosecuted," said Anthony Romero, the ACLU's executive director.

The issue isn't necessarily going away

Neither a truth and reconciliation commission, nor the issuance of preemptive pardons is likely to happen. No one will be prosecuted and many of those involved in the programme will be able to continue their careers at the CIA.

But that doesn't mean the issue is going away. Liberal activists may continue to agitate for more accountability, including the sacking of John Brennan, the current director of the CIA.

The question of torture could also be an issue for Hillary Clinton as she tries to win over the Democratic base ahead of the 2016 election. Ms Clinton, who once said torture might be acceptable in "very rare" circumstances, may come under pressure to promise stronger actions than those Mr Obama has taken.