SYDNEY, Dec 12 AAP - The family of a murdered NSW policeman say they have been "kicked in the guts" by a decision to slash the jail term of his mentally-ill killer.
Mitchell Barbieri was jailed for 35 years with a non-parole period of 26 after pleading guilty to the stabbing murder of Detective Inspector Bryson Anderson in 2012 at a Sydney rural property.
On Monday, in a majority decision, the NSW Court of Criminal Appeal allowed his sentence challenge and imposed a 21 years and three months term with a non-parole period of 15 years.
Speaking outside court surrounded by relatives and supporters, Det Insp Anderson's brother Warwick Anderson said they were not satisfied, but had understood, the original sentence for the "spineless and cowardly act".
"We came here today and were — to use my father's words — kicked in the guts by the decision that came down today," he said.
"How any informed member of the community could possibly think a sentence of 15 years for someone who stabs to death a policeman who turns up to help other people is what the community expects is absolutely beyond belief."
Barbieri, then 19, was sharing mental delusions with his mother, Fiona, when he stabbed Det Insp Anderson twice in the chest with a hunting knife during a siege at the pair's rural property in Oakville.
She was given a non-parole six-and-a-half years for manslaughter.
In cutting Barbieri's term, two of the three appeal court judges found the sentencing judge erred in applying principles relevant to the sentencing of mentally-ill offenders.
"His mental illness diminished his moral culpability to a very significant degree," said Justice Carolyn Simpson.
"His evidence persuades me that the applicant is genuinely remorseful, that he has accepted responsibility for his conduct, and that this indicates that he is unlikely to re-offend."
The appeal court also found Barbieri's sentence was disproportionate to that imposed on his mother.
"The circumstances of his life were such that he had not had the opportunity to develop even the maturity that might be expected of an average 19-year-old," Justice Simpson said.
"He lived alone on a rural property with a mentally-ill mother whose delusions he came to share."
Outside court, Scott Weber, president of the Police Association of NSW, described the court's decision as "disgusting" and called for an appeal.
"How can we say to (the family) have a Merry Christmas and have a Happy New Year. We can't."
But "this offender, this horrible person" would be out in 11 years after committing such a heinous crime.