A group of seven people, including Kirkwood, were charged over the successive assaults.
Narath Chourn, 34, was last month jailed for two years after admitting charges of manslaughter and unlawfully detaining Yean.
Chourn took Yean to the home where he would ultimately die after being confronted about contaminated drugs which had been brought for a New Year's Eve party in 2019.
One man died and several others were hospitalised after taking what they thought was Ecstasy, or MDMA.
The substance contained traces of heroin, but associates of the person who died sought retribution.
Yean's body was later found dumped on farmland near Gordonton.
Kirkwood was convicted by Justice Ian Gault who also issued a three strikes warning.
Kirkwood was remanded in custody for sentencing on August 26.
Meanwhile, the remaining accused - Neha Wiremu Grey, 38, Daniel James Payne, 32, Mihingarangi Tynneal Rameka, 26, Anton Rite, 25, and Teretere Raiha Te Aroha Taniwha, 20, will go on trial in October for their alleged part in Yean's death.
The group face a variety of charges including kidnapping, wounding with intent to cause grievous bodily harm, manslaughter, accessory after the fact of murder and murder.