There were any number of potential killers.

He sent word to the prison authorities.

He wanted to be moved to an isolation cell. And he wanted to talk to the gardai who were investigating the murder of Limerick bouncer Brian Fitzgerald. He has a lot to tell them, about that crime and any number of others, which he had been involved in since his teenage years. It was the only way he could think of to silence the voices. So began, on May 9 2005, the long process of unspooling the reel of a life that had lurched from violent crime to depravity, leaving a trail of destruction in its wake.

On Tuesday last, James Martin Cahill entered the main courtroom at Cloverhill courthouse in Dublin. He was preceded into the room by two plainclothes detectives. Three more followed directly behind him, along with two prison officers. The detectives took up position around the room. Cahill stepped up into the witness box and looked down into the well of the court.

At various times his eyes have sought out the four accused whom he claims were involved with him in planning and executing the murder of Brian Fitzgerald in Limerick on 29 November 2002.

All four deny the charge.

Cahill has confessed to shooting dead Fitzgerald as the latter returned home from working as a bouncer at a city nightclub. Cahill didn't know his victim. There is no suggestion that Fitzgerald had any association with criminals.

The Central Criminal Court has heard evidence that he became a target after he made a statement to the gardai which perturbed Mr A, the man whom Cahill says ordered the murder. Mr A can't be named for legal reasons.

One of the more confusing lines in evidence that was often extremely confusing was delivered on Thursday.

Under cross examination that day, Cahill said Mr A didn't order the killing. When discrepancies between his evidence and previous statements to gardai or psychologists are pointed out, he frequently refers to the "voices screaming in my head" when he was imparting the earlier information. "I'm being honest, " he repeats time and again. "I wouldn't want to see anyone wrongly convicted."

Cahill is a large, fat man, who is completely bald. He turned 28 on the day he murdered Fitzgerald. He speaks in a low, almost gentle voice, that belies the character of a violent, habitual criminal.

Frequently, over the course of his evidence, Judge Peter Charlton had to ask him to speak up or use the microphone.

He says he was paid 10,000 to do the job. He has described how he approached Fitzgerald as he got out of his jeep around 4am that morning. An argument ensued. Cahill shot him.

Fitzgerald attempted to run away. Cahill followed. As Fitzgerald lay on the ground, Cahill shot him in the head, just, he claims, as he was instructed to do.

Later that day, having fled to Belfast, Cahill says he met up with Mr A. "Did you see the shit run down his leg, " Mr A asked, according to Cahill. "I said I did, " Cahill told the court last week. "But it never."

He is serving a life sentence for the murder and is also in the witness protection programme following his offer to give evidence against the accused in this case.

"I was getting screaming about things I did when I was younger, " he told the court. "I was getting flashbacks. I could see the murder in pictures."

At one stage he thought the television in his cell was talking to him, saying, among other things, to "give him one in the head".

Behind a phalanx of lawyers . . . up to 17 on the defence side . . . the four accused sit, each sandwiched between prison officers. Five rows behind them, at the rear of the public gallery, Fitzgerald's widow Alice and two female companions attend the court every day.

Cahill claims 24-year-old Gary Campion drove the motorbike used to transport him to the murder. He says 50-year-old Anthony Kelly, who is from Kilrush, Co Clare, supplied the gun.

Kelly's son Joseph and Cahill were friends since Cahill came to live with an uncle in Kilrush when he was 15.

The other two accused are cousins of the man who Cahill claims ordered the murder. Dessie and John Dundon sit side by side each day, occasionally conferring. Cahill says they were involved in planning the killing, pointing out Fitzgerald to him at the victim's place of work, Doc's nightclub, and showing him where the bouncer lived.

His evidence has been peppered with inconsistencies which have been repeatedly pointed out by lawyers for the accused men.

Entry to the court is only permitted through a metal detector, manned by a number of gardai. More gardai mill around outside the building. On Tuesday, the first day of Cahill's evidence, members of his security detail insisted that no members of the public or press stand in the public gallery.

Even by the standards of what is known as gangland, his own account of his life and crimes is shocking. He was born and bred in Birmingham. He told the court on Thursday that his father was violent. He ran away from school under threat of being sent to a special school. When he was 15, he was sent to live with an uncle in Kilrush.

Over the course of a few weeks in prison, he compiled a 150 page account of his life and crimes. He has admitted to paedophilia, involving five children.

He told of how he punched his girlfriend, rendering her unconscious. He has recounted an occasion when he fantasised about having sex with a horse in Kilrush.

He has been involved in armed robbery, burglary, assorted thefts and threats to the life of gardai among others. While he was in solitary confinement, he assaulted a prison officer by throwing a kettle of boiling water on the man and then punching him. He says he thought the guard was going to kill him.

On another occasion, he refused to come out of his cell to meet with a psychologist in an interview room. The psychologist reported that he had to interview Cahill while standing in the doorway of his cell, as Cahill sat, naked but for a blanket, on a blue plastic mattress.

He was serving his original sentence in Portlaoise for possession of a machine gun, which he subsequently said was to be used to murder Dublin criminal Declan Griffin.

"You have led a brutal and brutalised life, " counsel for Campion, Conor Devally suggested to him on Wednesday. Cahill agreed.

He has told psychologists that when his sentence is served he would like to live in a house on the beach in Australia.

On Friday, counsel for Kelly, Michael O'Higgins, put it to Cahill that the voices were a convenient ruse when it suited him.

"Contrary to the gormless impression you are creating, you are a clever, clever liar, " O'Higgins said.

"I'm being honest, " Cahill replied.

The trial before a jury of 12 men resumes on Monday when O'Higgins is expected to complete his cross examination, the last of the four from lawyers for the accused.