Police believe the 10-year-old girl may have been murdered after she was abducted from her bedroom in West Hackham in 1983.

They are re-examining the backyard of another West Hackham home they first searched in 1991 when it belonged to convicted child murderer Dieter Pfennig.

Pfenning, who has not been named as a person of interest in this case, was jailed in 1992 for abducting and murdering a 10-year-old schoolboy whose body was never found.

Police say they have no information to share just yet but they continued their search on Friday.

Ground-penetrating radar equipment has been used to try to find clues to the fate of the girl whose body has never been found.

Raymond John Bolte, formerly known as Raymond Geesing, was sentenced to life imprisonment in 1983 for her murder and abduction.

His conviction was overturned by the Court of Criminal Appeal two years later and he was freed from jail.

He was later jailed again for sexually abusing two sisters over an eight-year period in the 1990s.

The evidence forms the backbone of the case against former schoolteacher Dieter Pfennig, 65, who was today charged with the murder of the 10-year-old schoolgirl.

In a sensational development in the 30-year old mystery, detectives from the Major Crime Investigation Section descended on Port Lincoln.

Pfennig, who has been a suspect in the Bell abduction for two decades, was taken to the Port Lincoln police station after being arrested and formally interviewed.

He was then charged with murder.

In an Adelaide Magistrates Court hearing before Magistrate Jayanthi McGrath, he appeared via videolink from Port Lincoln Magistrates Court and was remanded to next appear in February. He sat emotionless and silent.

The arrest was the culmination of a two-year cold-case review in which many pieces of evidence, including the pyjama top worn by Louise, were sent to the Netherlands by police for advanced DNA testing.

The pyjama top was left on the front lawn of a neighbour's house two months after Louise was abducted from her bedroom on the night of January 4, 1983.

The DNA testing used new "low-copy'' testing techniques that have been successfully used in other jurisdictions, including the US.

The low-copy method of DNA testing is a far more sensitive technique than the method used in Australia.

It can extract a DNA profile from just a few cells of skin or sweat.

The review also led to police excavating the backyard of a Hackham West house that was occupied by Pfennig when Louise was abducted.

It was the second time his house had been searched by officers investigating the case.

Deputy Commissioner Grant Stevens declined to be drawn on the nature of the new evidence against Pfennig, but said police would allege he abducted Louise from her bedroom sometime after 10.30pm on January 4.

They believe he acted alone and no other suspects are being sought.

"She has not been seen since and unfortunately her remains have not been located,'' Mr Stevens said.

"This is a significant step forward in the investigation and is evidence once again that police continue to investigate murders, regardless of their age or the difficulty of those investigations.''

Mr Stevens paid tribute to the current investigators and others, many of whom have since retired, who also sought to bring Louise's killer to justice.

"We have also had significant support from Forensic Science SA, who have been instrumental in helping us to bring this case to a point where we have been able to make an arrest,'' he said.

Louise was snatched from the bedroom of her house on Meadow Way during the night of January 4, 1983.

Neighbour Pat Golsby, who has lived in Meadow Way since 1971, welcomed news of the arrest.

"We all had young children at the time, there were a lot of children on the street so it was very distressing,'' she said.

"It is something that has needed to be solved for a long time and you just wonder all the time who could do such a thing.

"Our kids used to all play together, it would be nice to know where Louise is for her parents' sake. Hopefully now they can get closure for the parents. It has taken so long.''

Pfennig has been a suspect in the case for two decades. He lived two streets from the Bell house when Louise was abducted.

The backyard of his house and a shed were first excavated in 1991. The floors of two bedrooms were also dug up as part of the search, which failed to find any evidence.

One of the key exhibits sent overseas for forensic testing was the pyjama top Louise was wearing at the time she was abducted through her bedroom window.

Weeks after taking Louise, her abductor phoned Kathleen Smith - who lived near the Bells - and asked about medical advice for Louise.

He told her where to find Louise's earrings - under a brick at the Beach Rd-South Rd intersection. Earrings matching Louise's were discovered.

Five weeks later he left Louise's pyjama top - neatly folded - on Mrs Smith's front lawn.

Algae and soil samples found on the pyjama top led police to the estuary area at Noarlunga but no trace of the girl was found.

Deputy Commissioner Stevens said the arrest was the "culmination of the relentless work of all those police involved over the years combined with the dedicated efforts of Forensic Science SA personnel".

The investigation had involved taking 550 statements as detectives pursued Louise's murderer.

"Murder investigations never close and police do follow up every line of inquiry in the hope that each case is solved and the justice process completed," he said.

"Police have had ongoing contact with the Bell family during the past 30 years and continue that contact today.

"Louise's family remain devastated by her disappearance and remain hopeful that her remains will, one day, be found.

"Police will continue to work hard to meet this expectation. As this case shows it is never too late and police will take action whenever possible."

Raymond John Geesing, who had lived 500m from the Bell house until two months before her abduction, was initially charged with murdering Louise. Police had spoken to the father-of-four days after the abduction.

He was convicted using circumstantial evidence, but this was later overturned. The court found some grounds of suspicion but that they fell far short of the proof the law required for conviction of a criminal offence.

A key witness, a prisoner, was found to have fabricated his statement implicating Geesing, who successfully sued the government for facial injuries sustained during his 16 months in prison.

Louise Bell trial: Dieter Pfennig found guilty of murder

By court reporter Candice Prosser -ABC

Dieter Pfennig has been found guilty of murdering 10-year-old Louise Bell more than 30 years ago, in one of South Australia's most notorious cold cases.

The schoolgirl was abducted from her Hackham West bedroom, south of Adelaide, in January 1983 and her body has never been found.

Her disappearance prompted a police search of then unprecedented proportions.

Raymond John Geesing was initially tried and convicted of her murder but that conviction was quashed on appeal in 1985.
 

Pfennig was arrested and charged with Louise's murder in 2013 after advances in DNA technology led to a breakthrough during a review of the cold case.

The 68-year-old is already serving a life sentence with a non-parole period of 38 years for murdering Murray Bridge boy Michael Black in 1989 and later abducting and raping a 13-year-old boy.

Justice Michael David announced his guilty verdict to a packed public gallery full of family members, detectives and others.

He said in court that he wanted to "bring this whole ghastly thing to an end".

"I'm going to say something that's quite unusual, but I've thought a lot about it.

Louise 'likely enticed' through her window

Justice David said in his written judgement he could not say how she was taken from her room, whether she was dragged out through the window, enticed to come out, or was taken through the front door.

He said Louise's sister was very close in a "very small room" at the time of her abduction.

"Her parents were also in a small room divided from the girls' room by a very thin wall," Justice David said.

"Any form of forceful abduction would surely have woken another member of the household.

"I think it more likely that the accused to some extent knew the deceased through his daughter and enticed her to come out through the window."

'Tantalising gaps in evidence', says judge

Justice David said in his written judgement the "finding of guilt is not affected by the fact that we will never know some details of what occurred or the full story".

"There are many tantalising gaps in the evidence.

"I do not know how he actually killed the deceased, where he killed her, or where he put her body. These questions may never be answered, but they do not impinge upon the certainty of my verdict."

Sentencing submissions will be heard on December 6.

In a statement, South Australian Police said the case was "not closed" and appealed for any information which could lead to the recovery of Louise Bell's remains.

"I would appeal for anyone with information that might assist us to find her, to search your conscience and come forward now," Detective Superintendent Des Bray said.

"It is time to do the right thing."

Victory for Louise

Outside court, Louise Bell's father, Colin Bell, stood next to Detective Brevet Sergeant Anthony van der Stelt as the officer spoke to the media on behalf of the family.

"Today's verdict leaves us feeling relieved," he said.

"It has been a long time coming and while it's a significant outcome, it's not the end of this difficult journey."

The Bell family thanked police, prosecutors, Justice David, friends, family and supporters.

"It is a small victory for Louise," said Detective Brevet Sergeant van der Stelt.

Louise Bell trial: Judge's verdict long time coming in tragic mystery

By court reporter Candice Prosser- ABC

The brazen abduction of 10-year-old Louise Bell from her suburban home south of Adelaide on a summer's night in January 1983 was a mystery that captivated and horrified the community.

It led to a police search of then unprecedented proportions and shocked the public.

The unthinkable had happened — a little girl was abducted from her bedroom in a quiet, friendly neighbourhood, never to be seen again.

Raymond John Geesing was initially tried and convicted of her murder but that conviction was quashed on appeal in 1985.

Louise's abduction and murder remained a high-profile cold case and then advances in DNA technology led to a major breakthrough three decades later.

The schoolgirl's yellow pyjama top, which was left at a nearby house a few weeks after her disappearance, became one of the most vital clues in the case.

In 2011, after a cold case review, samples from the clothing were sent to the world-leading Netherlands Forensic Institute.

And in November 2013 former school teacher Dieter Pfennig, who was already serving a life sentence with a 38-year non-parole period for murdering 10-year-old Michael Black in 1989 and later abducting and raping a 13-year-old boy, was charged with Louise's murder.

A Supreme Court judge today delivered a guilty verdict after Pfennig's trial, which began in September 2015 and finished in July 2016.

It delivered more than a few surprises and was a widely anticipated court case.

'A dad, teacher' likely enticed Louise from bedroom

Defence lawyer Grant Algie said Louise's disappearance was "a bit like South Australia's Azaria Chamberlain, where the public was shocked, outraged and horrified but also intrigued and drawn into the speculation of how this could happen".

But how it happened is a question we are never likely to know the answer to.

Prosecutor Sandi McDonald said as much in her closing address.

"At the end of the day, Your Honour might well, in fact it's likely, arrive at the point where you just don't know how it occurred."

She said given the difficulties in physically getting a 30 to 40 kilogram child out of her bed and through the window without waking up Louise's sister, who was sleeping in the same room, the most likely scenario was that Louise was enticed out of her bedroom.

Ms McDonald said it was "far more likely that she has gone with someone she knows, someone she recognised, a dad, a teacher, than a stranger".

Pfennig, according to the prosecution, fit that bill.

He was then a teacher and he knew Louise. She had played basketball with his daughter.

Pfennig continued to maintain his innocence and the prosecution was put to proof on all aspects of their case.

The unusual challenge to the DNA evidence involved several special late sittings with video links to some of the world's best minds in the field, including Professor Peter Gill.

Such a calibre of expert witnesses was a unique and fascinating aspect of Pfennig's trial.

His lawyers were challenging the validity of the DNA evidence, pointing to differences between results obtained from the South Australian Forensic Science Centre to those obtained from the Netherlands Forensic Institute.

The DNA evidence obtained from Louise's pyjama top came from three sources; a piece of fluff, a stain and tape-lifts.

The court heard in precise scientific detail about the testing process in the Netherlands which resulted in a likelihood ratio of more than one in a billion.

That was in stark contrast to the likelihood ratio of 6,400 to one that was generated in the Adelaide laboratory.

Professor Gill said he was not at all surprised there was such a difference in the results, saying it was "a bit like comparing apples and pears" because of the different techniques used.

He said such a variation was not scientifically problematic.

After initiating such a fiercely contested defence to the DNA results, Pfennig's legal team then abandoned the challenge and sought to put forward an explanation to how Pfennig's DNA could have got on the 10-year-old's pyjamas.

They said it could not be excluded that the DNA could have ended up on Louise's pyjama top through a process known as secondary transfer, whereby DNA is passed on to a person through another person such as Pfennig's daughter who played basketball with Louise.

Pfennig obsessed with girl's disappearance

As important as DNA evidence often is, Ms McDonald pointed out that it was not the be-all and end-all of the prosecution case.

She said the case amounted to so much more; it also involved a so-called "trail of evidence" spanning decades.

"That trail was in how he behaved, what he did, what he said and what he left behind him," Ms McDonald told the court.

There were allegations Pfennig had demonstrated somewhat of an obsession with Louise's disappearance and spoke about it often.

Tellingly, according to the prosecution, he had once told a colleague he was a suspect in the murder before he was ever considered to be one.

"Why on earth would a father, teacher, a family man be telling his colleague and friend that he was a suspect in the abduction and murder of a little girl when he's not?," Ms McDonald said.

There was evidence Pfennig had continued this obsession to discuss the case, resulting in alleged jailhouse confessions to two inmates on separate occasions.

That led to some very interesting cross-examination.

Jailhouse confessions under spotlight

One of the former inmates, whose identity is suppressed, was called to give his account of Pfennig's alleged confession which he claimed happened when Pfennig became emotional after smoking cannabis with him about Christmas time.

When he was challenged during cross-examination by Mr Algie, the witness reacted by repeatedly calling the lawyer derogatory terms including "twit", "ferret" and "homeboy".

After being asked by Mr Algie if he was lying and was just giving evidence to get attention, the witness responded "whatever, homeboy" and later told Mr Algie to "f*** up, idiot".

"You're all a bunch of clowns in here, seriously ... I hate all of youse. You're not my friends. I just want to get on with my life and hope you will all just f*** off, seriously," he said during his evidence.

He later became a key focus of the defence case; in fact their only witness was a forensic psychiatrist who was called as part of a defence attempt to discredit the witness.

The psychiatrist testified the man had a severe anti-social personality disorder with characteristics of narcissism and manipulative behaviour of being "cocky", "hostile" and "sarcastic".

However, when cross-examined by Ms McDonald the psychiatrist agreed the disorder would not necessarily affect a person's reliability.

The other witness who testified about an alleged jailhouse confession was an ordained Baptist minister who claimed Pfennig had confessed to murdering Louise in the context of seeking spiritual guidance and counselling.

The prosecution submitted the two alleged admissions were completely separate, there was no opportunity for the witnesses to collude and both went to police before the DNA results pointing to Pfennig were obtained.

A lengthy prosecution case combined with two separate arms of Pfennig's defence, one relating to the DNA evidence, resulted in many different sittings and adjournments in the trial, a luxury best afforded in judge-only trials.

At one stage the whole process looked as though it may be derailed when Pfennig suffered a heart attack in prison and was rushed to hospital.

However, he was back in the courtroom within two weeks of his heart surgery and the trial continued.

More than 33 years after Louise disappeared from her bed, the judge's verdict is a long-awaited outcome.