A toddler died in a Southland house just five days after social workers sent him back there from hospital, despite knowing it was unsafe, records show.
The mother's partner, who pleaded not guilty to murdering the 17-month-old boy, was found dead in custody five weeks later.
The man was only in the house because Child Youth and Family approved him being there.
All identifying details of the victim, partner or mother, including their names, have been suppressed by a court ahead of an inquest later this year.
The child's father and his family believe CYF failed the boy. They provided RNZ with emails and correspondence with officials, showing some of what happened, though the documents are redacted in many places.
However, the documents show social workers twice cleared the man to live with the boy and his preschool sister near Invercargill, in the weeks and days before the boy's death.
The boy was found dead in his bed at home in October 2015 and the man was charged soon afterwards.
The man's own family had raised warnings about him, saying he had been a good father to his own children but had begun using methamphetamine again and behaving violently in early 2015, after his children moved to the North Island.
When his family found out he had moved in with the victim's mother and her two children, they alerted the children's father, who called CYF more than once saying he feared for their safety.
However, the father was in prison for assaulting the woman, and the records show CYF and police downplayed his warnings.