Bermuda's laws on sentencing murderers should be reviewed so judges can fix the length of time they spend in jail, a prosecutor argued yesterday.

Crown counsel Cindy Clarke made the point during the appeal of Dennis Robinson against his life sentence for murdering the Cooper twins, together with Kenneth Burgess.

Burgess beat 20-year-old Jahmal and Jahmil Cooper, bludgeoning them with a metal baseball bat at his Devonshire apartment in March 2005. The attack was said to be in revenge for them allegedly robbing his father.

Robinson guarded the door to prevent escape and then helped Burgess to dispose of the bodies down Abbot's Cliff in Hamilton Parish.

The pair failed earlier this year to get their convictions overturned. Both had been jailed for life for the double murder, by the Chief Justice in 2006. By Act of Parliament, that meant each must serve a minimum of 15 years behind bars before the Parole Board can consider them for release.

If the Parole Board never deems them safe for release, the men could die in jail.

Robinson's lawyer, John Perry QC, argued during the course of this week's appeal that the 15-year proviso is unconstitutional, because Parliament infringed on the functions of the judiciary by setting it.

It is, he said "depriving the citizen of his liberty in circumstances where it's not imposed by the court. The deprivation of liberty by a body other than the court is instantly unconstitutional – is instantly in breach of sections three, five and six."

The sections of the Constitution he was referring to are protection from inhuman treatment, from arbitrary arrest or detention and the right to the secure protection of law.

Mr. Perry said that because there is no statutory provision for judges to set the length of a sentence, they cannot do so in Bermuda.

Since his appeal hinges on the technical issue of whether the current sentencing rules are correct, Mr. Perry has not outlined what he feels the appropriate sentence for Robinson ought to be.

However, he made it clear to the Court of Appeal that Robinson played a lesser part in the double murder, and should therefore be entitled to a shorter period behind bars.

"I think we all agree, standing back as human beings in a human situation, it seems clear Mr. Robinson has got a raw deal," he remarked yesterday.

Ms Clarke contested Mr. Perry's arguments. She said the mandatory 15 years in prison, as set by Parliament, is not unconstitutional. However, she told the Court of Appeal that a judge should be able to fix the length of a sentence going upwards from that.

Ms Clarke said the Crown does not view the law on murder sentences as it stands as "perfect" because it leaves the question of length open. She explained: "I do believe there should be some amendment to allow the discretion of the sentencing judge to make it clear."

She told the panel of three Appeal judges that the problem is that while Bermuda adopted part of the Canadian criminal code that sets a mandatory minimum sentence, it did not adopt another part of the code that allows a judge to set a sentence within a minimum and maximum range.

In Canada, a judge can fix a sentence in murder cases of ten to 25 years.

She told the judges that at the time of sentencing Robinson and Burgess, the Crown asked that in contrast to Robinson, Burgess should have his sentence fixed at more than the minimum of 15 years. This failed, she said "because the Chief Justice did not have an express power to increase it".

Referring to the fact that Bermuda lacks the section of Canadian law where a judge could fix a term within a minimum and maximum range, she said: "It would have saved us all quite a bit of time, with respect, if it had been put in".

This should, she argued, be clarified by Parliament.

The judges reserved their decision, but did not set a date for when it will be delivered.