Corrections Minister Judith Collins says a knife found hidden in the cell of convicted killer Graeme Burton was brought in from outside and is not a prison-made knife.
The pocket knife was found at Auckland Prison at Paremoremo during a search at the end of June.
In 2007, Burton was jailed for killing Karl Kuchenbecker in the hills of Wainuiomata while on parole and tried to kill a fellow inmate by stabbing him with a sharpened steel rod the following year.
Burton previously served 14 years in prison for murder over a fatal stabbing outside a Wellington nightclub in 1992.
Ms Collins says only a few people are allowed access to Burton's cell and she hopes prison staff were not coerced into getting the knife to him.
The minister says the Department of Corrections is working hard to make sure it investigates everything and every contact who could possibly have been manipulated by Burton.
Burton is classed as an extremely dangerous prisoner and has no contact with visitors or other prisoners.
The department says daily cell checks are part of its management plan for Burton and staff are required to sign off each one. It is investigating whether the plan was being followed.
Fewer violent incidents, says Collins
Public Service Association national secretary Richard Wagstaff, whose union represents about a quarter of prison guards, says the problems with weapons are only going to get worse if the prison system is not properly resourced.
Mr Wagstaff says policies such as the three strikes policy seem to result in locking people up for longer, which increases the risk in prison as people who have no hope of early release have no incentive to improve their behaviour.
However, Corrections Minister Judith Collins says staff safety is a high priority and there are now fewer violent incidents at Auckland prison, compared with three years ago.
She says as a result of the find, dangerous prisoners are now subject to more stringent searches.
Ms Collins says prisoners will always attempt to make weapons, but the ban on smoking and reducing access to razor blades will make it a lot harder for inmates to fashion weapons.
Prison dangerous for many inmates - lawyer
The lawyer representing Burton says jail is dangerous for many inmates, such as those not affiliated to gangs, and prisoners will attempt to get weapons for self-defence.
Peter Tomlinson told Morning Report weapons are found regularly in high security prisons.
Mr Tomlinson says prisoners who are locked in their cells for up to 23 hours a day will find some way to create a weapon out of whatever is available, and more needs to be done to occupy them.
