A former CIA operative has revealed his methods for extracting information from detainees and the secret prison they were taken to.

Glenn Carle, who has written a tell-all memoir about his time with the agency, said some people would call him a 'torturer.'

He maintains he carried out all his duties within the law and within the boundaries of what he believed was morally right.

In The Interrogator Carle recalls the time after 9/11 when he was assigned to get information out of a suspected senior member of Al Qaeda.

At first Carle tries to build a rapport with the man he refers to in the book as CAPTUS.

When this doesn't work the agency send the pair to 'Hotel California,' a so-called 'black site' or secret prison in an undisclosed foreign country, according to the book.

There CIA interrogators work long hours while heavy metal music blasts detainees' ears and their sleep patterns are disrupted, according to the book.

'The objectives are to "dislocate psychologically" a detainee,' Carle told Wired.com.

'This is done through psychological and physical measures, primarily intended to disrupt Circadian rhythms and an individual’s perceptions.

Clandestine: Carle reveals the CIA sent him and detainee CAPTUS to 'Hotel California,' a so-called 'black site' or secret prison in an undisclosed foreign country (file picture)

Methods: Psychological and physical measures are used on detainees in order to disrupt Circadian rhythms and an individual's perceptions, Carle said (file picture)

So, noise, temperature, one’s sense of time, sleep, diet, light, darkness, physical freedom - the normal reference points for one’s senses are all distorted.

'Reality disappears, and so do one’s reference points. It is shockingly easy to disorient someone.'

Carle writes in the book how he came to believe that CAPTUS was in fact innocent, and how it was not necessarily what the CIA wanted to hear.

He left the 'black site' after 10 intense days but feared his psychological manipulation of CAPTUS meant he was in fact a torturer.

Disorientated: Noise, temperature, one's sense of time, sleep, diet, light, darkness, physical freedom - the normal reference points for one's senses are all distorted, during interrogation

Revelations: Carle has written about his time in the CIA in explosive memoir The Interrogator

'I opposed all these practices and this approach,' Carle told Wired with reference to the methods used at the prison.

'I was involved in it, although I tried to stop what I considered wrong.

'I feel I acted honourably throughout my involvement in the CAPTUS operation, and tried to have him treated properly, but much of it was disturbing and wrong.'

The CIA released CAPTUS eight years later without ceremony or explanation. 

Despite the secret prison being almost in a no-man's land in terms of legal implications, Carle said he never could act with impunity.

'We were acting clandestinely; but never beyond obligations to act correctly and honourably,' he said.

'The dilemma comes in identifying where those lines are, in a situation in which much was murky.

'No one consciously broke the law, ever, in my experience or knowledge,' he added.

'But what should one do? How could one follow one’s orders and accomplish one’s mission, when it was flawed, objectionable, and perhaps itself legally, albeit "legally" ordered.

'That’s the supreme dilemma I wrestled with, and others did, too.'

So-called 'enhanced interrogation techniques' for use on high-value detainees were approved in 2003, according to declassified documents.

These included: the attention grasp, walling, the facial hold, the facial slap, the abdominal slap, cramped confinement, wall standing, stress positions, sleep deprivation beyond 72 hours, the use of diapers, harmless insects and of course, water boarding.

Carle maintains he never used any of the above methods.

'I would not do it,' he told Wired. 'That point I was certain of instantaneously. I also had literally never heard of waterboarding until the story about it broke in the media.'

The CIA edited about 40 per cent of the first draft of his book, Carle said.

'One would infer, obviously, that large segments of the agency would have preferred to leave CAPTUS’ story in the dark, where it took place,' he added.

Perhaps tellingly, when asked how may CAPTUS'S - seemingly innocent men - there were being interrogated by the CIA, Carle said: 'I do not know.'