Road-rage killer Kenneth Noye has launched a High Court battle to be moved to open prison conditions.
Noye, now 69, was convicted of murder in April 2000 and sentenced to life with a minimum term of 16 years.
He stabbed 21-year-old electrician Stephen Cameron to death in a road-rage attack on the M25 in Kent in 1996.
After the killing Noye went on the run and was arrested in Spain two years later.
In September 2015 the Parole Board declined to order his release, but recommended that he be transferred to open conditions.
But the board's recommendation was rejected by the then justice secretary Michael Gove.
A judge in London is now being asked to rule on whether the rejection decision was "unlawful and irrational".
Edward Fitzgerald QC, for Noye, told Mr Justice Lavender at a hearing on Thursday that the tariff period had now been served, and the "sole issue is the issue of risk".
He argued that "the Secretary of State has failed to give proper or adequate weight to the recommendation of the Parole Board and is therefore unreasonable and contrary to law".
Mr Fitzgerald told the judge: "It is conceded that it is ultimately for the Secretary of State to decide if a prisoner should be transferred to open conditions.
"However, the claimant submits that the Secretary of State's reasoning for rejecting the Parole Board's recommendation does not stand the test of scrutiny."
Noye's judicial review challenge is contested by current Justice Secretary Liz Truss, who argues that there was "nothing irrational" in the decision taken.
Tom Weisselberg QC, for the Justice Secretary, said Mr Gove had decided he would "personally take the decision on transfer and would not leave the decision to his officials".
He said: "He was rightly concerned about a decision which would have the effect of undermining public confidence."
The decision not to transfer was made as the result of a number of factors, the court heard, including Mr Gove's "doubts as to the credibility of the claimant's claims" that he had "changed his attitude to violence", the "risk of absconding posed by the claimant's links to Spain", the "risk of violence linked to the claimant's ego and desire to be in control", and his "use of excessive violence".
In 1985 Noye stabbed police officer John Fordham 10 times. A jury found him not guilty of murder or manslaughter on the ground of self-defence.
Mr Weisselberg submitted: "The Secretary of State was entitled to consider that the claimant had made excessive use of violence, even where the jury acquitted him of murder, particularly in circumstances where his decision had the potential to put members of the public at risk."
The QC argued: "The Secretary of State was entitled to consider the risk to the public posed by the claimant and to decide that further work needed to be done by the claimant in closed conditions before a transfer to open conditions would be appropriate."