Justice Mander said he had no doubt that if staff hadn't fled the building, or if staff weren't fortunately absent that morning, there would likely have been more fatalities.
They were "cold-blooded executions", particularly callous and brutal, he said.
"This type of crime is rare in New Zealand," Justice Mander said.
Justice Mander said Tully was a "very dangerous person" who was very capable of extremely violent actions.
He held a high risk of harm, which meant that there is a need for the community to be protected.
Today, a Court of Appeal spokeswoman in Wellington confirmed that Tully has formally lodged an appeal against his conviction and sentence.
No date for any hearing has yet been set.
Throughout the court process, Tully always indicated he would always appeal whatever the outcome was.
At sentencing, he alleged a "major cover-up by the Crown" regarding disclosure and evidence, and further claimed he didn't have access to a lawyer.
Tully sacked at least six defence counsel.
"If I was guilty and went out and killed two people, I'd take it, and say, 'That was me'. But obviously that was not the case and I refute the accusation," Tully said.
Tully was found to be mentally capable of facing charges of double-murder and attempted murder after a hearing under the Criminal Procedure (Mentally Impaired Persons) Act 2003 in the High Court at Christchurch last year.
