Zaoui and Bain at jail bash

The Corrections Department has been forced to explain why two staff members attended a work Christmas function dressed as a suspected terrorist and accused mass murderer - both of whom have been inmates in New Zealand jails.

The pair's colleagues could have been forgiven for thinking Algerian asylum seeker Ahmed Zaoui and former prison inmate David Bain had crashed their end-of-year bash. But the pair were simply Corrections staff masquerading in costume - "in David Bain's case it involved no more than a rather large cardigan" - for a themed party where head office staff dressed up as their favourite notable New Zealanders.

The National Party's Corrections spokesman Simon Power says the workers' choice of dress was irresponsible given their role in a government justice organisation.

But Corrections' chiefs are defending the fancy dress outfits, saying the pair were juniors and not directly involved in managing offenders, even though most staff went as sportspeople.

"In the context of a staff Christmas party, I don't think it matters a jot," Corrections acting chief executive Phil McCarthy said. It would be different if the two workers were employed as probation officers or warders, or had had contact with the former inmates, he said.

However "they're as likely to have been a clerk or information officer".

Asked what the pair's costumes had consisted of, Mr McCarthy said: "In David Bain's case it involved no more than a rather large cardigan" - a probable send-up of the former Dunedin paper boy's patterned jerseys which he became known for wearing while accused of gunning down his family.

Mr McCarthy did not know how Ahmed Zaoui had dressed but said "a certain physical resemblance" was thought to have been the biggest motivation for the costumes.