He also faces a charge of attempted murder.
The co-accused's brother-in-law said he'd wanted to see how the weapon "performed".
He is due to appear in the Manukau District Court later today.
The trial began on Tuesday, more than three decades after the murder of Chris Bush.
She is one of three staff members to give evidence.
The case remained unsolved until 2017.
Publican Chris Bush was gunned down during an armed hold-up at the Maramarua pub.
He faces a non-parole period of 19 years.
More to come.