The Ministry of Social Development has been convicted for failing to take all practicable steps to protect its staff - a matter which came to light after the double-murder in 2014.
The prosecution was brought by WorkSafe which began investigating the ministry after double murderer Russell John Tully stormed Ashburton's Work and Income office on September 1, 2014, fatally shooting 67-year-old receptionist Peggy Noble and 55-year-old case manager Susan Leigh Cleveland as she begged for her life.
Tully, 50, was also earlier this year found guilty of attempting to murder case manager Lindy Curtis.
He is currently serving at least 27 years in prison.
Chief District Court Judge Jan-Marie Doogue held a sentencing hearing in the Wellington District Court on Monday but reserved her decision until today.
She entered a conviction against the ministry but said a fine could not be imposed as it was a Crown organisation. If she had been able to impose a fine, it would have been $16,000 to reflect the "lower band of culpability".
The ministry pleaded guilty earlier this year to breaching the Health and Safety Act, but disputed some allegations.
It accepted five of the six practicable steps which WorkSafe alleged it failed to take, but did not accept the first step, which was ensuring there was no physically unrestricted access by clients to the staff working area.
The ministry did not agree with WorkSafe's interpretation of what a safe office layout should be.
Following a disputed facts hearing in July, Judge Doogue released a decision finding the ministry should have taken such a step.
She said in her earlier decision client-initiated violence in the office was predictable, but noted while some form of physical barrier might have delayed Tully, she did not believe it would have stopped him.
In the sentencing yesterday, defence lawyer Brett Stanaway argued for a discharge without conviction for the ministry, but WorkSafe prosecutor Dale La Hood said the application failed "at the first hurdle".
He said the application failed at balancing the gravity of the offending with the consequences of a conviction, and that a conviction would not affect the ministry in any practical way.
La Hood said the hazard with the office layout was "obvious", there had been "sustained client violence" over a period of time, and in ministry chief executive Brendan Boyle's words, client initiated violence was "inevitable".
"The ministry's own experience told it that clients with weapons posed a great risk of serious harm," he said.
"Victim impact statements indicate a culture within the Ashburton office of putting up with, or allowing, or making employees put up with a level of intimidation from clients that caused staff anxiety and consequential emotional harm."
He said changes to make the office safer were "not difficult or costly to implement".
State Services commissioner Peter Hughes said the judgment "has implications for customer service delivery across the state sector and the steps that need to be taken to keep staff and visitors safe".
"The safety of our staff and the people visiting government service centres is an absolute priority," he said.
"At the same time we also need to ensure government offices are places where New Zealanders can feel comfortable and work constructively with the public servants who are there to help them.
"Brendan Boyle has my full support for the work he has done responding to what happened in Ashburton and its aftermath, and the leadership he has shown on behalf of MSD and the whole public service," Hughes said.