In an exlusive interview with Times Online, Neil O'May, the lawyer for Sion Jenkins, looks back on six years of the Billie-Jo Jenkins case Neil O'May, the lawyer for Sion Jenkins, has lived and breathed this case for six years.

Looking back after the former deputy headmaster was acquitted at a third trial for the alleged murder of Billie-Jo Jenkins, his foster daughter, O'May said: "I personally feel a huge weight has been lifted off my shoulders that's dominated part of my work for the past five to six years, something that always presented ? if not on a weekly then a daily basis ? new problems and new difficulties. It very much feels the end of an era."

O'May, a partner with Bindman & Partners, a leading firm in the area of human rights and miscarriages of justice, was not involved in the original trial and was brought in at the appeal stage after a recommendation by Bob Woffinden, an investigative journalist who had sat in on the appeal following Jenkins' conviction in 1998. "He felt it needed a fresh approach," O'May said. Having started what I thought was a relatively limited appeal, I was almost overwhelmed when it became an an enormous appeal covering all the science and original evidence through to the re-trial."

In the early stages, there were periods of inactivity and O'May had the back-up of a team of four or five other lawyers working on the case so he "had time to do other things". But once the re-trial began, in the summer of 2004, the defence of Jenkins ? which O'May did on legal aid ? became an almost full-time job.

From the start, he was struck by the failings in the original trial. "I could see, very early on, that something awful had gone on," he said. Three things hit him. "The first was the very simplistic and also dogmatic scientific evidence that was produced at the first trial." The second was that Jenkins' two eldest daughters, Annie and Lottie, had not been called to give evidence. "This was because the defence had been wrong-footed about what they might say."

The pair had been video-interviewed immediately after the murder by the police and given their father an alibi. "But subsequently," O'May recalled, "while Jenkins was on bail and the case was running to trial, representations were made by his then wife, Lois, to the police as to what the girls were then saying which appeared to be different. The defence was then unable to ascertain exactly what they might say because for one reason and another they were unable to gain access to them." The trial was then went ahead and the opportunity was not pursued, he said.

The third factor that "had great impact" on O'May was that Jenkins himself ? for tactical or other legal reasons ? did not give evidence in chief; he was only cross-examined by prosecuting counsel. "He was only asked: did you murder Billie-Jo? He then gave the answer 'no', and sat down."

But that meant that the court was deprived of the opportunity to hear the defendant's story, in his own words, O'May said. "It was my view that in such a case, the defendant must be asked to tell his story, in the atmosphere and in the theatre of the court room, where the court had heard from a number of prosecution witness? that the defendant must be allowed to give his own account of coming across Billie-Jo. But the prosecuting counsel did not allow him to give that account of his emotions, and what happened. So you have a very clear distinction: the human prosecuting witnesses, and the apparently cold, calculating defendant. But that was a function of the theatre of the court as much as of the questions that were asked."

The failure of two further juries to agree a verdict after the original conviction has prompted questions about the role of juries in such cases. O'May is an ardent supporter of the jury system. But he argues that it was almost impossible for Jenkins to have a fair trial after all the press coverage.

The indecision of the jury, he believes, stemmed from what he saw as "a large amount of prejudicial coverage after the first trial" ? comments on Jenkins' fabricated CV, for instance, "none of which could be countered because he was convicted."

O'May: "That's what a lot of people remembered, every time the case came up, that solidified in their minds, so everyone came to the court with a view ? and that view, generally, was 'guilty'. There was a large bandwagon, people saying: you remember that case, that's the one where he lied, and that cemented his guilt."

But once in the courtroom, the issues were debated in an even-handed way and on the basis of the evidence, with strong arguments for and against, he said. "And some of the jurors, at least, were able to deal with those issues in that kind of way. But others, frankly, could not do that. And that's why you end up with a hung jury. It was more a failing of the criminal justice system as anything else ? that he could not have a fair trial. And that's the problem of having a trial nine years after an investigation."

But even before trial, things had gone wrong for Jenkins. O'May is critical of the police investigation, believing the police did not pursue other lines of inquiry as vigorously as they could have, or other potential evidence that, "with hindsight", they could have pursued. The forensic evidence led the police to believe that the minute traces of blood on Jenkins' clothes had resulted from the impact of a blow, whereas the defence argued that these resulted from nose exhalation."So the forensic evidence drove ? almost from the start ? the way the police investigation went."

One piece of evidence O'May believes was to prove crucial for Jenkins' defence, however, was that the killer had stuffed a black bin bag up Billie-Jo's nose as she was dead or lay dying "with such force that it was difficult to pull out again." The act "speaks volumes about the kind of person who would do that to another?..this was the inexplicable by the prosecution, that Sion Jenkins could have the motivation and the opportunity to do that, then wash his hands in the time available."

O'May is now considering what, if any, next legal steps to take. He will be seeking compensation for his client's "nine lost years", and is also exploring whether there are other legal avenues against the police or prosecuting authorities for wrongful conviction.

In one sense, he acknowledged, Jenkins is fortunate: his background gave him the contacts and know-how to mount a campaign against his conviction in the first place; an opportunity denied others who are less well-connected. He had a huge amount of support thorugh the "Justice for Sion Jenkins" campaign and that helped, O'May said.

"If you don't have access to investigative journalists in that way, that is one problem. The other is that under the legal aid system, how do you get decent lawyers to review convictions? There's a limit to the amount of pro bono work a legal aid lawyer can do, to do it properly."

Looking back, he said his worst moment was after the appeal, when he was served with the prosecution papers. "I realised that all the concessions we thought we had won had been rejected and and we would have to push that boulder all the way up the mountain again."

The best moment was when Jenkins got bail. "Because whatever you think of prison, the moment when someone gains his or her liberty, and realises what they have lost, is a very emotional moment. It always drives home what a profound thing loss of liberty over a period of time is."