Wellington Que' />

A top lawyer has been appointed to review Scott Watson's petition to be pardoned after his convictions in the Sounds murder cases.

Wellington Queen's Counsel Kristy McDonald has been hired by the Ministry of Justice to advise the Minister of Justice on Watson's formal request for freedom.

Watson, who was convicted of the murders of Ben Smart and Olivia Hope in 1998 and sentenced to a minimum non-parole period of 17 years, wrote a 22-page letter to the Governor-General in November.

He asked Sir Anand Satyanand to pardon him under the royal prerogative, on advice from the Ministry of Justice, or for the case to be reheard by the Court of Appeal.

Justice Minister Simon Power can decline the application, refer the case back to the Court of Appeal, or grant a full pardon.

Ms McDonald would not comment on the Watson case to the Weekend Herald.

In his letter, Watson said the case against him had dissolved and no longer existed.

"A miscarriage of justice occurred in R v Watson and this is now undeniable," Watson wrote.

"I am innocent of the murders of Ben Smart and Olivia Hope and had no part in their disappearance."

As part of his petition, Watson enclosed a copy of Auckland journalist Keith Hunter's book Trial by Trickery and award-winning documentary Murder on the Blade?

Defence lawyer Greg King said the jury accepted the evidence at the original trial but evidence produced since was the key to overturning Watson's convictions.

Ben and Olivia were last seen boarding a yacht moored off Furneaux Lodge in the Marlborough Sounds in the early hours of January 1, 1998.

In his letter, Watson said a new jury would hear that:

Police witnesses Guy Wallace and Roz McNeilly had recanted their evidence of picking Watson from a photo montage.

A secret witness had recanted his evidence that Watson confessed to him while in jail.

Sailing speed tests had shown it was impossible for Watson to have been seen in Cook Strait when police say he was there.

There was no evidence to prove Watson made two trips to shore on the night Ben and Olivia disappeared, a key claim in the 13-week trial.

Dozens of sightings had been made of a two-masted ketch which Wallace was adamant he had taken Ben and Olivia to but which police said did not exist.