Maxine Carr's application for early release from jail was rejected today.
The ex-girlfriend of Soham killer Ian Huntley had been put forward for a Home Office electronic tagging scheme by the governor of Holloway Prison in north London.
But today prisons chief Martin Narey used new powers to overrule that decision, a Prison Service spokesman said.
The Prison Service released a letter sent to Carr by Mr Narey which explained his decision was based both on "the issue of public confidence" and the risks to her safety at the address at which she proposed to live.
Under the home detention curfew (HDC) scheme, prisoners are fitted with an electronic tag and trigger alarms if they leave their home during the curfew.
In direct response to Carr's application, ministers introduced new powers last month to overrule prison governors' decisions to grant early release.
They granted Prison Service chief Mr Narey the ability to refuse release on the grounds that it would undermine public confidence in the tagging scheme.
Mr Narey's letter to Carr said: "I have now considered the question of your suitability for release on HDC and have decided that you should not be released under the scheme.
"Although not charged with murder, your offence was considered so closely related to the events surrounding the murder of the two girls and the police investigation that followed, that you were tried jointly with Ian Huntley.
"Your conviction for conspiring with Ian Huntley to pervert the course of justice connects you indelibly with this case and with the public outcry that has accompanied it.
"For this reason, the possibility of your early release on HDC has attracted, and continues to attract, huge adverse publicity.
"I have therefore concluded that for the above reasons your release on HDC, so soon after the trial has ended, would undermine public confidence in the HDC scheme."
Mr Narey's letter went on: "There are two reasons for my decision.
"The first reason relates to the risks to your safety at the HDC address you have proposed.
"The second reason relates to the issue of public confidence in the HDC scheme."
The spokesman said Carr's solicitors were given the opportunity to argue why her release would not undermine public confidence.
"Their views were taken into account by Mr Narey before he made his decision," he added.
Carr, 26, was sentenced eight weeks ago to three-and-a-half years for conspiring to pervert the course of justice after Huntley murdered 10-year-olds Holly Wells and Jessica Chapman.
She has been in jail since August 2002 and would stay behind bars until mid-May if she were to serve half her sentence.
Ed Willetts, governor of Holloway, had approved Carr's application to join the scheme.
She became eligible for release in early January and would have walked out of jail within a matter of days if Mr Narey had approved the application.Reuse content