Prisons Unlocked. Panorama tracks down convictred drug smuggler Christian Ekkebus who walked out of an open prison in the UK.
Dangerous criminals are being placed in low security open prisons due to overcrowding, at "massive" risk to the general public, the BBC has learned.
Colin Moses, of the Prison Officers Association, told Panorama he feared prisoners were not "properly assessed".
Justice Secretary Jack Straw said: "All prisoners located in open conditions have been rigorously risk assessed."
The UK prison population - more than 90,000 - is at an all time high and the system is at breaking point.
The concerns expressed by Mr Moses are shared by the National Association of Probation Officers (Napo).
It is unacceptable these institutions are coming under such pressure to take unsuitable prisoners that we see the risk of absconds and therefore a risk to the public
Shadow justice secretary
"I've certainly been worried for 15-18 months that individuals are being transferred into open jails who pose a risk to the public" said Napo's Harry Fletcher.
"The worry is they are not being properly assessed," he said.
That increases the risk of dangerous and violent criminals walking out of low security prisons and carrying out further serious crimes.
Panorama has learned that over the last decade there have been almost 14,000 cases of prisoners leaving open jails without permission.
They are not all inmates serving short sentences for minor offences.
Government statistics reveal more than 130 murderers have absconded from the open estate in the last ten years.
"It is unacceptable these institutions are coming under such pressure to take unsuitable prisoners that we see the risk of absconds and therefore a risk to the public," said shadow justice secretary Nick Herbert.
Panorama investigated the case of a convicted murderer who walked out of an open prison in Scotland and killed again.
The BBC programme also tracked down a Dutch drug trafficker, Christian Ekkebus, serving a ten year sentence, who failed to return from weekend leave and is now back living in his native Holland.
Justice Secretary Jack Straw would not agree to an interview for the programme, despite repeated requests .
However, in a statement he stressed public safety was paramount.
He said: "All prisoners located in open conditions have been rigorously risk assessed."
The director of Scottish Prisons, Mike Duffy, admitted more 'difficult' prisoners were being put into open jails.
"We are planning and programming more for difficult prisoners to try and ensure they don't return to crime in the future," he said.
But he categorically denied a link between prison overcrowding and unsuitable prisoners being pushed into open conditions.
But those at the front line of the prison system disagree.
"We need to go back to rigorous risk assessment," said Mr Moses.
"The other side of that is we put people in open conditions, they abscond, and continue their criminality. That puts everyone at risk".
Panorama: Prisons Unlocked will be on BBC One at 8.30pm on Monday 5 May 2008.
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