Dieter Pfennig pleaded not guilty at the start of his trial in the South Australian Supreme Court on Monday with prosecutor Sandi McDonald telling the court it was alleged Pfennig had admitted taking and killing Louise to fellow prison inmates on two separate occasions while in jail for other offences.
Ms McDonald said in a conversation with one inmate, Pfennig said: "I did it. I took her. It was an accident. I killed her."
He indicated to another inmate that "I know where she is."
The court also heard that a comprehensive review of the case in 2012 resulted in DNA samples taken at the time the girl went missing in 1983 being subjected to testing both in Australia and in the Netherlands.
She said the chances of a random male providing such a match were greater than one in one billion.
The crown's opening on Monday included details of how a neighbour to the Bells took a phone call from a man not long after Louise went missing which led police to find the girl's earrings which had been placed under a brick near where she went to school.
The same neighbour found the girl's pyjama top, which had been left folded near her home.
Pfennig is alleged to have taken Louise from the bedroom of her parents' home at Hackham West on the night of January 4, 1983, but was not charged until 2013.
Ms McDonald said while the girl's body had never been found, after more than three decades it was not possible she was still alive.
"Louise Bell is dead, she was murdered, she was taken from her bedroom in the middle of the night, in the most brazen and audacious way," she said.
The trial continues.
THE LOUISE BELL MURDER CASE:
• The disappearance of 10-year-old Louise Bell in 1983 is one of SA's most enduring cold cases.• Former maths and science teacher Dieter Pfennig, 67, has pleaded not guilty.
• The Crown says it has DNA evidence linking Pfennig to the girl.
• The Crown alleges that while Pfennig was in jail for other offences he told fellow inmates he had killed the girl.
• The court has heard how a phone call made by a man after Louise went missing led them to find her earrings under a brick near where she went to school.
• Louise's father Colin Bell has told the court how he last saw his daughter after he put her to bed on the night she went missing.
• The Supreme Court trial before Justice Michael David is sitting without a jury.