Convicted double murderer John Barlow now has a nervous six-week wait for the law lords at the Privy Council in London to decide his fate.
Five law lords of the Commonwealth's highest court overnight heard the last hour of the appeal hearing for Barlow.
On the first day of the hearing, Barlow's lawyer Greg King rubbished FBI forensic evidence that led a jury to send his client to prison.
After twice going through trials that ended in hung juries, Barlow was jailed for the murder of Wellington father and son Eugene and Gene Thomas, who were killed in 1994.
Mr King's first victory was for the law lords to hear the petition for special leave to appeal, and to consider evidence the New Zealand Court of Appeal would not hear when it denied Barlow an appeal in March 2008.
After the first day of the hearing yesterday Mr King said: "All we ever asked for in this case was for the opportunity for the case to be considered on its merits - and we've been successful because the Privy Council has given us that.
"We've been asking for that to happen for years but that has been denied us in New Zealand by the Governor-General and the Justice Minister."
Mr King told the law lords that crucial evidence relating to the weapon and bullets that killed the Thomas' had been falsely linked to Barlow, a former antiques dealer, who is serving 14 years in Upper Hutt's Rimutaka Prison.
Mr King said evidence given by FBI agent Charles Peters had been proved to be flawed and that had unduly influenced the jury at Barlow's third trial, after juries failed to reach a verdict at two previous trials.
Mr 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 Crown case in all three trials hinged on proving that Barlow's CZ27 pistol, and related bullets and a silencer, was the murder weapon.
Before Mr King left New Zealand he said the Privy Council had four options:
* Refer the case back to the Court of Appeal in New Zealand;
* Quash the convictions and leave the New Zealand courts to decide whether to try the case again;
* Quash the convictions and acquit Barlow, which would mean the matter would be at an end;
* Or reject the appeal.