KEY POINTS:
Further doubt has been cast on the evidence of an FBI expert who convinced jurors to convict John Barlow of double murder at his third trial.
After two hung juries, Barlow was convicted of the 1994 execution-style shootings of Wellington businessman Eugene Thomas and his son Gene after the ballistics scientist gave fresh evidence at a third trial in 1995.
Charles Peters testified that forensic testing known as comparative lead bullet analysis showed bullets found at the crime scene matched those belonging to Barlow.
But the tests have since been discredited worldwide for providing a high number of false matches.
The Privy Council in London last week granted leave for Barlow to appeal against the double murder conviction, a ruling his lawyer Greg King described as "huge".
King, the Wellington barrister who took the case to London for a two-hour hearing, gave the Herald on Sunday exclusive access to the documents handed to the law lords.
They disclose a "revelation" of "enormous significance," said King, that Peters had never found an "analytically indistinguishable" bullet match in years of testing before or after the Barlow trial.
Giving evidence in a United States trial in 1997, Peters said under cross-examination that a bullet match had been found just once - in the Barlow case.
"The failure to disclose before trial anything in respect of the FBI database was therefore of major significance in this case," King wrote in his petition to the Privy Council.
"Mr Peters' own testimony at the subsequent trial seriously undermines the value of the conclusion that he gave at [Barlow's] trial.
"Serious resulting prejudice is therefore demonstrated in that the jury was completely misled."
The Crown case in all three trials hinged on proving that Barlow's CZ27 pistol was the murder weapon.
The defence argued Barlow loaned his gun and bullets to Eugene Thomas, who wanted them to defend himself, weeks before the murder.
On stumbling across the bodies of Eugene and Gene Thomas, Barlow thought the older man had used the gun to kill his son, then himself, in a murder-suicide.
Panicking, Barlow, who is serving life in Rimutaka Prison, took the gun and fled the scene.
Earlier this year, Governor-General Anand Satyanand refused his appeal for a retrial, on advice from the Justice Ministry and Justice Minister Annette King.
The case is the third double murder case King has taken to the Privy Council. The others were appeals for Bruce Howse and Scott Watson.
Leave was granted for an appeal hearing in the case of Howse, who was convicted of murdering his stepdaughters in Masterton in 2001, but a retrial was not granted.
In 2003, King was unsuccessful in his application for an appeal against Watson's convictions for the killings of Ben Smart and Olivia Hope, who disappeared in the Marlborough Sounds in 1998.
More than $570,000 of taxpayers' money has already been spent on legal aid for Barlow - the third-highest total in New Zealand history.
TOP 10 LEGAL AID BILLS
* $1.3 million and counting - David Bain, accused of murdering five of his family members
* $623,000 - Convicted double murderer Scott Watson
* $570,000 - Convicted double murderer John Barlow after three trials and an unsuccessful appeal
* $286,463 - Timothy Taylor, convicted of killing Christchurch hitch-hiker Lisa Blakie
* $269,055 - Convicted rapist Malcolm Rewa
* $265,754 - Convicted child sex offender Peter Ellis
* $257,402 - Danny Condren, acquitted of murder
* $233,030 - Richard McFall, convicted after a four-month drugs trial
* $212,317 - William Haanstra, acquitted of murder
$211,721 - Convicted murderer Colin Bouwer
