The handwriting was minuscule, the paper as flimsy as airmail.

I had written to Moors Murderer Ian Brady as research for Myra, Beyond Saddleworth, the novel I was writing, but somehow had not expected a reply. As I turned his first letter over in my hand, I was half scared to open it, wondering what kind of a man it would reveal.

If someone has done the things Ian Brady has done, murdering five young people for his sexual pleasure, there are certain assumptions you can make. He is probably not going to be a likeable person, and he is certainly not going to be trustworthy. I decided that I would weigh up anything he said and use my own judgement as to whether it was the truth or not. That proved to be a sound instinct. In a later letter Brady even denied the sexual component of the murders, saying it was police invention when the bodies of some of his victims were found naked or in sexually provocative positions.

As I slit the envelope of this first letter a little slip of paper fell out, recording that it had been read by an officer at Ashworth secure mental hospital, where Brady is being held. His writing swarmed across the page, fluent despite its minute size. And angry. There was a huge feeling of rage from Brady's words, mostly about the regime at Ashworth, which he hates with a passion, and about politicians. People like Tony Blair and George Bush, he declared, had as much blood on their hands through their imperialistic wars as he ever did.

However much you loathe those two politically – and I do – there's a world of difference between what they did and what Brady and Hindley did: kidnapping young people and taking them to the bleak wastes of Saddleworth Moor to murder them, as happened to Pauline Reade, John Kilbride and Keith Bennett, taping the torture and murder of a little girl, Lesley Ann Downey, or hacking 17-year-old Edward Evans to death with an axe.

But I couldn't deny that there was a strange kind of rationality in the thought, a cold logic which said that, in terms of number of deaths caused, Brady lagged behind. It seemed to enrage him that the Establishment was not reviled for their misdeeds as he had been for his, a theme that was to continue throughout our correspondence. In one letter he talks about the release of Churchill's wartime menus, which "show him slurping bottles of whisky, champagne [and] brandy with every sumptuous meal, while the underclass fought and starved for the privilege of poverty and unemployment. Thankfully, the Germans bombed Glasgow back to full employment. Even in the 1960s Earl Mountbatten was prosecuted for adding water to the milk on his farm so you can imagine how the landed gentry 'rationed' themselves during the war".

The common stereotype of a serial killer is a cold-blooded psychopath, a person with a void at their centre, but Ian Brady wasn't empty – he seemed to be seething away inside, with a restless and relentless energy that, because it did have its own logic, drew the reader into his way of thinking. I, of course, was agreeing only with an intellectual premise, but it made me realise how powerful Brady must have been in person, how he must have used his fierce intelligence to convince Myra Hindley to join him in the murders.

She already fancied the tall, dandyish Scotsman. Once she was admitted into his private world, she clearly had no wish to withstand the malign energy at his core.

In that first letter Brady agreed to talk to me in exchange for what he called a "quid pro quo". Although he writes to many people, he doesn't reply to everyone. Perhaps it was the Glasgow address that made him agree. Born illegitimately to a young waitress, Peggy Stewart, he grew up in Camden Street in the Gorbals, where he was adopted by the Sloan family. He has enormous affection for the Glasgow of the past and wanted me to send him photographs of certain places from his childhood. It turned out that Camden Street no longer exists and many of the old buildings had been knocked down, so the pictures, which my brother took for me, showed bleak modern streets with mediocre council flats, quite unlike the handsome tenements of old.

Over the years Brady and I have exchanged many gifts. One of his first to me was a compilation of film music, most notably the soundtrack to Natural Born Killers, with Leonard Cohen's song, The Future, whose lyrics are so subversive that in the televised performance of his last UK concert tour Cohen himself neglected to sing one of the most powerful lines, "Give me crack and anal sex". To be cooking in your warm kitchen and suddenly hear Cohen's gritty voice intoning

Give me back my broken night

My mirrored room, my secret life

It's lonely here,

There's no-one left to torture

Give me absolute control

Over every living soul

And lie beside me, baby,

That's an order!

knowing that those words had been sent to you by a man who lived them was truly chilling, so much so that I used it as the epigraph for the novel. Afterwards I wrote to him and said he had a very black sense of humour. I never knew whether that amused him or not. As with everything he doesn't want to answer, including details of the murders, he simply ignored the remark.

I always send him something at Christmas, often something warm as I feel he must be cold given the number of years he has been on hunger strike. Years ago a journalist described Brady hugging a stone hot water bottle to his stomach, and that was when he was still in prison, still eating. He has been on hunger strike for the longest time in British penal history, possibly in the world. Since September 1999, when, he claims, he was physically manhandled from his room by prison officers dressed in riot gear, he has refused to eat and is forcibly fed in a tedious process that takes two hours twice a day.

Psychiatrist Chris Cowley, who visited him several times in Ashworth, described the chair he sits in as being encrusted with the dried-in yellow liquid they feed him. It is a mark of Brady's ferocious will that he continues to put up with the boredom and sordid surroundings - most people resume eating after a while, but he is convinced of the rightness of his cause and will not give in. His body is one of the few weapons of protest he has, after all – although not much attention is paid to the opinions of a multiple killer.

His gifts to me have been striking: one was a reproduction of an 18th-century etching of skeletons fighting, sent in response to my saying I was looking for images for cards I was producing of my short 'flash fiction' writing. Unsurprisingly, none of my mini-stories quite fitted that image.

Brady also gave me a Sony Walkman that he wanted me to hand on to a charity. I tried several, but when they heard of the machine's provenance they refused it, a decision I find shameful on their part. I believe that whatever people have done, we should treat them with the dignity they have denied their victims, although it's an attitude I know can make people uneasy. Deborah Orr of the Guardian said she found my attitude to Brady "shockingly protective": "your kindness to him, sending things to feed his nostalgia, cheer him up".

Yes, I have sent him many postcards of old Glasgow, of the steamie at Partick, one of a drinking cup at Glasgow Green which set him off about drinking cups in general. They often triggered off memories and small details which I would use in my novel. Quid pro quo. But the public in general seem uneasy at the idea that people like Brady and Hindley are anything less than monsters. Many people criticised writer and journalist Gitta Sereny, for example, for getting "too close" to her subjects, particularly Mary Bell, the child killer who was herself only a child when she murdered.

I wouldn't claim to have got too close to Brady as I have no idea whether he enjoys our correspondence or has any sense of me as a person. But he has definitely touched me as a person. Early on in our correspondence he said that he never used the word "remorse". He thought it was useless, that we should show remorse by our actions. He set up a braille unit in prison and spent years translating books for the blind. That does not come close to making reparation, but, I believe, implies an acknowledgement at least of the enormity of his actions, a small form of restitution. For a man who sought ecstasy and the perverted thrills of sexual murder when he was free to embrace such tedium in captivity implies, I think, a sense of guilt.

Later he also sent me a DVD of a children's film, The Amazing Mr Blunden. It starts off with a scene of children playing in the street and singing a song that all children must die. Was this another example of Brady's black humour? As the film progressed I began to see that it was a powerful parable about remorse. A ghost, Mr Blunden, is haunted by guilt about ignoring a cry for help from his two wards, who were subsequently killed in a fire. He persuades two modern children – the film is set in 1918 – to go back to Victorian times to try to change what happened that night. This time the children are saved and it is Mr Blunden who dies in the fire.

Cynics would say that Brady is a manipulative psychopath, that he's playing me for a fool. And of course he might be. Perhaps he's a good enough judge of character to know that I would be very affected by the film and feel a deep sense of pity for him. He was certainly astute enough to recognise in Myra Hindley a woman who would share his sexual longings and bind herself to him unquestioningly. But in fact I don't think he does understand people particularly well. He made a huge error of judgement in the last killing, of Edward Evans, when he thought his disciple David Smith would be like Myra and follow him unthinkingly into the blackness of murder. Instead, Smith went to the police. You have to wonder whether he likes people enough to understand them?

"Trivia and pettiness consume mankind, surely the most pretentious creation of all," he wrote to me recently.

And much of what he says appears to be ill-judged fantasy. In his latest letter he talks about his criminal connections after another of his correspondents "revealed" that Brady had been connected with Glasgow crime overlord Arthur Thompson: "I began cultivating professional contacts in Strangeways at 17, mixing with adults while waiting three months for sentence to Borstal and continued for the next two years of captivity, cross-referencing exchange of information."

The grandiosity of his language here strikes me as quite inappropriate, as if he doesn't sense how it will come across to the reader. After all, his criminal gang in the end consisted of him, his girlfriend, and a younger bloke who turned him in. Not exactly the criminal empire he dreamed of creating.

Throughout our correspondence he has seemed perfectly sane to me, although he doesn't think he'll be granted his wish to be judged so and rails against the authorities' power to exclude, restrict and censor evidence: "Against such political/bureaucratic organised criminal interests I never expected to be allowed to win anyway."

I have found him to be a complex and powerful man who, despite having been cooped up alone for so many years, is fluent, rational and interested in politics, music, film and ideas. But he's angry, angry, angry. Perhaps it is insane to be that angry all the time. It was certainly deadly for his victims.

Myra, Beyond Saddleworth by Jean Rafferty is published by Wild Wolf Publishing and is available in trade paperback and Kindle editions