Everything seemed straightforward. The woman was young and single, had faced her first pregnancy alone, and now wanted to give her baby son up for adoption. It was a sad, but not particularly unfamiliar, story. Her boyfriend hadn't been at all pleased when she conceived, didn't want anything to do with the child and had now finished their relationship, she'd said. She felt she had little choice.

Perhaps all that was really needed was to rubber-stamp the application and get on with the next case. But Borovnik, only two weeks into his first permanent posting with the then NSW Department of Community Services (now the Department of Family and Community Services, but still known by its old acronym, DoCS), was keen to make sure all the t's were properly crossed and the i's dotted, and called the hospital where the child had been born to confirm all the details with nursing staff. And it was that fateful phone call on July 8, 1999, that triggered the first of a series of alarm bells.

"The nurse told me that the woman had said this was her first pregnancy," says Borovnik. "But they said it was strange: the doctors reported that it really didn't look like her first baby. When they'd examined her, they'd felt sure she'd had a baby before."

Borovnik decided to run some checks to make sure this baby boy really was the first child this woman had given birth to. What followed was a six-year investigation; an inquest into the disappearance of a child; one of the biggest searches for a missing person ever conducted, both here and overseas with the help of Interpol; criticism of inexplicable delays in the police handling of the case; national changes in the laws regarding birth registration; and eventually, in 2010, 11 years after Borovnik's first phone call, the conviction of Sydneysider Keli Lane on a charge of murdering one of her babies. Her appeal against that conviction starts on Tuesday.

It's been a decade-long nightmare that's wrought havoc on the lives of nearly everyone involved. Lane is in prison, having had a bail application pending her appeal refused. Her marriage has disintegrated and the one child she did keep after giving birth is in the care of Lane's heart-broken parents. The judge who presided over her trial, now retired NSW Supreme Court Justice Anthony Whealy, says he has misgivings about the verdict. And John Borovnik, after ignoring orders from his bosses to drop the case in its early days, has left the profession he once loved, suffering an anxiety disorder and depression. He has since developed multiple sclerosis, an illness sometimes associated with stress.

"But I don't regret a thing," says Borovnik, now 51. "To me, I was doing my job. I made some inquiries and discovered there was something missing. To my horror, I discovered it was a child, a child by the name of Tegan. After that, it was all about finding justice for Tegan. My work is all about protecting children and it was terrible to think this child had been born and then no one had even noticed that she'd disappeared. I wanted justice for Tegan, whatever the outcome of the case itself. I wanted her to be recognised and acknowledged as every child in Australia should be."

The facts of the strange case of Keli Lane are by now well known. She was the young water polo champion from Manly in Sydney who had five pregnancies between 1992 and 1999 that she managed, incredibly, to keep completely secret from her family, her friends, her teammates, even her boyfriends. They resulted in two terminations and two babies being adopted out, while Tegan, the second baby, went missing and has never been found.

At her trial in 2010, Lane, then 35, insisted she'd given the child away to the father, a man called Andrew Morris, or Norris. A massive police hunt failed to locate father or child and the jury, in an 11-to-one verdict, found her guilty of murder and of lying under oath. In April 2011, she was sentenced to 18 years in prison.

Her appeal, set down for a two-day hearing, is being led by Winston Terracini, SC, who will argue that the jury should have been instructed that manslaughter and infanticide were alternate charges to murder. "We think a couple of the grounds we have are very, very good," he says. The appeal could result in an outright acquittal, a retrial, or a continuation of the status quo.

Borovnik has never spoken publicly before about his role in the investigation. That's understandable. He was always very aware that he has a colourful past himself and, in the case against so-called "golden girl" Lane - the daughter of a respected police officer, an admired sportswoman with Olympic ambitions, a teacher at a top girls' high school and a popular member of the local community with countless friends and supporters - he feared he'd be no match for her.

And maybe, in normal circumstances, that would be correct. As a new and unproven child-protection worker with a humble background of doing odd jobs after leaving school at 15, a victim of child abuse himself and a reformed drug and alcohol user trying his best in a department that was poorly resourced, the odds were stacked against him. But on his side he had one very valuable weapon: an unerring determination to do his very best by Tegan, the child he felt everyone else seemed to want to forget.

Borovnik's passion, even today, is obvious. He was the person responsible for having a plaque in memory of Tegan put up by the NSW Homicide Victims' Support Group in Ebony House, where the relatives of murder victims go for respite. He also has Tegan's name tattooed on his right arm, not far from the faces of his own two children, which are inked on his chest. "I suppose that's the one advantage of having MS," he says grimly. "I've lost a lot of feeling in my body, so tattoos don't hurt at all." And during the upcoming appeal, he's determined to turn up early to nab a seat in the courtroom opposite Lane.

During Lane's original sentencing, she looked once over to her parents and brother sitting nearby, and once up to the public gallery where Borovnik sat. She stared at him long and hard, and he returned that look. "From her, it was a gaze of pure hatred," said an onlooker afterwards. "If looks could kill ... From him, well, he couldn't disguise his relief."

At one point in the sentencing, Borovnik became uncomfortable when Lane's new boyfriend, teacher Patrick Cogan, took a seat behind him. At that, Borovnik moved to a position where he was flanked by police officers. The former DoCS worker's importance to the proceedings were lost on no one, including the senior Crown prosecutor in the case, Mark Tedeschi.

"John Borovnik was a most diligent DoCS worker who was the first to discover that Tegan Lane was missing," says Tedeschi. "He was relentless in his insistence that there be a full investigation by police of Tegan's disappearance, wherever that would end. Without John's involvement, her disappearance may well have gone unnoticed."

John Borovnik is a tall, lean man with a closely shaven head and a slight limp from a not completely successful left knee replacement. He looks tough, but is gently spoken and painfully polite. On a good day, his hands shake slightly when he talks. On a bad day, he can barely get out of bed. His MS is of the relapsing-remitting kind and it's taken a terrible toll on him physically since he was diagnosed in 2008. He's currently on a daily dose of a powerful immunomodulating drug to cut the number of relapses, but already has 17 lesions in his brain and five or six in his spinal cord. He has large areas of numbness all over his body and is in constant pain.

Back in 1999, he was a comparatively well, fit man of 38, much more muscular than he is now and a keen sportsman who played competitive soccer and was once invited to trial for a second-division English team. He'd had problems, but felt he'd overcome them. Physically and sexually abused as a kid, he found refuge from the age of 14 in alcohol and drugs and, after leaving school in year 10 in 1976, drifted from job to job, working as a storeman, delivery driver, in a foundry, doing renovations ... In 18 years after leaving school, he had no fewer than 39 different jobs.

In January 1994, however, he decided he wanted to do something more with his life. "The drink and drugs helped make me comfortable, they numbed the pain and the anger I felt," he says. "I'd hurt my knee when I was 20 and was told I'd never play sport again, and I was in constant pain from that, too. But I realised that trying to escape it all was getting me nowhere. I checked myself into rehab. They told me there that only one in 10 people make it through clean at their first attempt; some go back to drugs, some overdose, some die. I was that one in 10.

"I had some counselling, too, which helped a lot, and I realised I really wanted to give back. I hadn't come from a good place myself, but I could help make the world a better place for other kids."

Borovnik enrolled in a two-year welfare course, to take an associate diploma in social sciences and community welfare. He received a distinction. Part of his course involved doing fieldwork with DoCS in Katoomba, in the Blue Mountains west of Sydney, and in June 1998 Borovnik was given a permanent placement with the department as a child protection worker in Mount Druitt, a disadvantaged suburb in Sydney's west. The following year, in June 1999, he was transferred to Katoomba, and shortly afterwards the file about Keli Lane landed on his desk.

In all applications for adoptions, adoption agencies and the social-work departments of the various states and territories act together for the good of the child. It was the role of DoCS, in the case of a young mother wanting to give up her son for adoption, to check that all was well, and to apply to the children's court for a care order, giving foster parents the legal right to look after a child pending the finalisation of any adoption.

When Borovnik called Ryde Hospital, he was surprised by the nurses' disclosure of the doctors' doubts about Lane's pregnancy and started scouring the hospital records. There he discovered that a pregnant Lane had attended the same hospital three years earlier, saying she was overdue and asking to have her baby induced. The staff had examined her and assessed her as being only 38 weeks pregnant rather than the 40 she claimed, and discharged her. Three days later, she returned to Ryde, this time saying she was 41 weeks and three days' pregnant and again asking for the birth to be induced. She was given an ultrasound and, based on the results, discharged again. She turned up again the following day saying she had terrible back pain and asking to be induced. For the third time, staff refused.

This perplexed Borovnik. It seemed Lane had given birth to a child before, but was now lying about it. Why? And what had happened to that child? His curiosity was now piqued and he made a number of inquiries with the adoption arm of Anglicare and DoCS's own adoption branch, and discovered she'd had a daughter adopted out through Centacare in 1995. He reported his suspicions to someone more senior in the department, but they told him he'd obviously solved the mystery, and to move on to his other casework.

It could have all ended there, but for Borovnik's instinct that there was more to it. "There was something about it that still didn't feel right," he says now. "There were a lot of questions I had, and there didn't seem to be any rhyme or reason for this woman's behaviour. It just didn't stack up."

Borovnik continued his own painstaking investigation, grilling staff at several hospitals, contacting the Department of Immigration and the British High Commission (because Lane had said she'd been living in the UK), and seeking information from the Nurses Registration Board, the NSW Midwives Association, various adoption agencies and the NSW Health Department's Centre for Epidemiology & Research.

Soon, he found that the one baby was actually two different children: Lane's first, born in March 1995 at King George V Hospital in Camperdown and adopted out through Centacare Adoption Services; and her second, Tegan, born - after Lane was turned away from Ryde - at Auburn Hospital on September 12, 1996. Moreover, he learnt that Lane had supplied an incorrect address, had given the name of a midwife who didn't seem to exist but later turned out to be the mother of a boyfriend, and had never lived in the UK.

In October 1999, he finally phoned Lane at her workplace, the Ravenswood School for Girls in Gordon, on Sydney's wealthy upper north shore, and confronted her with his findings. Lane admitted having had one child before, and adopting her out, but denied all knowledge of a second child, Tegan. Borovnik told her he had to notify police. A few days later she faxed him, asking him not to contact anyone without letting her know.

Shortly afterwards, he reported the matter to Katoomba police, who referred the case on November 7 to Manly detectives, who in turn were impressed by Borovnik's investigation. (When his files were presented to the children's court in relation to Lane's son's adoption proceedings - the adoption that first alerted Borovnik to missing Tegan - the magistrate commented that he would have made a great detective, while the solicitor in court jokingly compared him to Perry Mason.)

Coincidentally, Lane's father had been a senior officer at Manly before he retired. At the time the case was transferred, Manly police were the subject of a covert inquiry by undercover officers into alleged corruption, turning a blind eye to drug dealing in exchange for regular cash payments. (There were no allegations made against Robert Lane.) It's not known exactly why they took so long to interview Keli Lane, but that didn't happen until February 14, 2001.

The investigation started, but then stalled again. Borovnik grew more anxious. Increasingly obsessed by the idea the child may have met with foul play, he vowed that her short life wouldn't be allowed to pass without trace. "She had no voice of her own," he says. "Others have to speak for her. I wouldn't be silenced. I was told at work to let it be, that it was in the hands of police. But nothing was happening, so I needed to push."

Finally, another detective, Richard Gaut, was appointed to the case in October 2002. Working initially with the evidence supplied by Borovnik, Gaut started gathering more and referred the case to the then NSW coroner, John Abernethy.

The inquest began in 2005, with Borovnik the star witness. In February 2006, the coroner praised Borovnik for his diligent work, said he was satisfied that Tegan was deceased, and passed the case back to the police. In 2008, it was given to the homicide squad's cold case team, who re-interviewed Borovnik. On the day in 2010 when police finally called Borovnik to tell him that Lane was to be charged with murder, he sank his head into his hands and wept.

As well as her critics, Keli Lane also has her supporters for the appeal. While most of her friends have now deserted her - "Whether or not she did it, she lied to us all about the pregnancies," says one, who asks not to be named - there are others who've come to her aid. Lane's boyfriend Patrick Cogan is one who's convinced she didn't kill Tegan. "It's been a difficult time for us, but we're hopeful about the appeal," he says. "We're as strong as ever together. We'll get through this okay."

Then there's prominent lawyer Chris Murphy, who's engaged two private investigators to look into Lane's case in a bid to uncover evidence of her innocence. "I've been a lawyer for 40 years and to my mind this is one of the worst miscarriages of justice I've ever seen," he says. "The trial should have been terminated and there wasn't enough evidence to convict her."

Wendy James, who wrote a novel, The Mistake, inspired by Lane's story, believes it's all a mess. "There's something terribly wrong and sad and desperate about her," she says. "I think the jury must have been affected by the storm of media about her. Regardless of what she did, I'm sympathetic to the way she's been treated."

Monash University ethicist Dr Leslie Cannold feels similarly. She sees Lane as a victim of moral panic, in the same way the mothers of Azaria Chamberlain, JonBenét Ramsey and Madeleine McCann were pilloried for failing to live up to an idealised vision of womanhood. "If women don't behave in a way we think is maternal, we think they're bad," says Cannold. "When someone breaks those rules of behaviour, we really come down hard on them."

Borovnik, however, feels that whatever happens in the appeal, at least there's been some recognition of a child who deserved to be accounted for. "As a result of all this, people did take Tegan seriously," he says. "We don't know if she may have suffered in her short life, or what happened to her. But now, finally, she has made herself heard. Her life had meaning and relevance, and that's what was always important."

Lead-in photographs of John Borovnik by James Brickwood.

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