The head of the Ministry of Social Development acknowledges not all possible steps were taken to protect staff at its Ashburton office.
Two staff members, Leigh Cleveland and Peggy Noble, were shot dead by Russell Tully in the office in 2014.
A third staff member was wounded.
Yesterday the ministry was convicted in the High Court by Justice Jan Maree Doogue of breaching workplace safety laws.
Although the ministry was convicted, as a Crown organisation it could not be fined.
Worksafe says the prosecution cost $258,000 and was justified because it was important to establish accountability and get clear guidance for the future.