It is understood that Brown, sentenced to life for murder at Glasgow High Court in 1976, was due to appear before a parole board within a month or two.

Had the board been convinced Brown had addressed his problems and was no longer a threat to the public, he might soon have been walking out of the open prison without needing to look over his shoulder.

Prisoners sentenced to life are always released under licence, which means they can be recalled to complete their sentence should they violate terms of that licence.

In the case of Brown, he will not only have to answer to a sheriff for his decision to abscond, but will also suffer the consequences arising from a breach of his life licence — and that could potentially add years to his sentence.

Brown’s decision to flee from the Carse of Gowrie prison has left in-mates and prison staff bewildered. Some questioned whether he has become “institutionalised” and unable to face up to the prospect of being released back into normal, civilian life. If so, it would not be the first time that Castle Huntly in-mates have defied logic by going on the run just weeks before they were due for release.

Today, the Scottish Prison Service adhered to its policy of refusing to discuss details relating to any prisoners.

However, a spokesman said that for some prisoners who betrayed the trust placed in them upon their transfer to an open prison the consequences could be dire. He said, “It is very disappointing when people abscond and there can be serious consequences for them.

“They go through a very rigorous process of assessment before they go to the open estate. Several hundred prisoners progress to the open estate every year and most respond well.”

The SPS has always said that when a prisoner is sent to the open estate the decision at that time was correct. The service said it has to balance the need to rehabilitate and prepare the prisoner for release with the need to protect the public.

The prisoner’s offence or offences are fully acknowledged when considering him for the open estate. If approved, prisoners must participate in prison programmes and undertake a staged return to normal life through escorted visits outwith the prison. At every step, the prisoner's response to the programme is assessed before any decision is taken.

There can be any number of reasons why a prisoner might abscond and these usually become apparent once he has been recaptured.

The SPS said that, in the case of prisoners failing to return to Castle Huntly, Tayside Police is usually notified within an hour of their non-appearance.

Responsibility for tracking down the abscondee then lies with the force. The two bodies consult before deciding whether or not the public should be notified about absconders.

This process takes into account the risk posed by the individual, current information about their whereabouts and the wider public safety.