A detective who worked as a family liaison officer during the Soham murder investigation lied to police about images on his laptop, a court heard.
Brian Stevens and Louise Austin are on trial at the Old Bailey
The prosecution allege Det Con Brian Stevens was aided by Louise Austin who said he was not present when "questionable images" were downloaded.
At the Old Bailey, they deny a joint charge of conspiracy to pervert the course of justice.
The couple were charged last September after an West Midlands Police inquiry.
Peter Joyce QC, prosecuting, said Mr Stevens, 43, gave a false alibi to police after he was accused of downloading the images, described in court as being "questionable", onto his laptop.
The officer was accused of using his computer to download the images in the early hours of the morning while he was being treated for a foot injury at a police officers' rehabilitation centre.
He and Miss Austin, 32, a case worker for the Crown Prosecution Service in Cambridgeshire, then concocted a story that he was elsewhere when the
images were downloaded, said Mr Joyce.
Mr Stevens was at the centre in Goring-on-Thames between 31 May and 10 June 2002.
Mr Joyce said the images had been downloaded in a 12-minute period in the early hours of Sunday 9 June 2002 .
Story 'suddenly changed'
Mr Stevens was interviewed eight times by police after his arrest three months later when his laptop was seized from his Cambridgeshire home.
Mr Joyce said the officer had denied all knowledge of images found on his computer.
"He said he had his computer with him and left it in his room and he said
other people had had access to it," Mr Joyce said.
Mr Stevens told police the computer had been left on almost continuously and that he had allowed other people to go into his room and use it when he was not there.
Mr Joyce added that on 8 August 2003, nearly a year after Mr Stevens was arrested and charged in relation to the images, his story "suddenly changed".
In a defence statement signed by Mr Stevens he said the laptop had not been with him during his stay at the rehabilitation centre.
In the new statement, he also said that he had spent the night the images were downloaded at Louise Austin's home and was not at the rehabilitation centre.
'Blizzard of communication'
Mr Joyce told the court: "So his story had totally changed since 'yes I was there at Goring with my computer' to 'I didn't have my computer and I wasn't there
Mr Joyce said Miss Austin had provided a witness statement to police which covered Mr Stevens for the relevant times.
"She gave a very detailed account as to how Brian Stevens came to be at her home, what they did whilst he was there and why she was able to remember it so well."
Mr Stevens counselled the family of schoolgirl Jessica Chapman who was found dead with her friend Holly Wells near the Cambridgeshire village of Soham in August 2002.
Mr Joyce said there was "overwhelming evidence" that the officer was at the rehabiliation centre when the images were meant to have been downloaded and there had been "a blizzard of communication" between the two of them between 1 May and 21 August 2003 which showed "the conspiracy in action".
Ian Huntley, the school caretaker, was jailed for life for the murders of the schoolgirls.
The hearing continues.