Threatening to kill the children and then commit suicide is a classic tactic of men seeking "power and control" over their partners, two experts say.

Waikato University psychologist Dr Neville Robertson and retired law professor Ruth Busch, who wrote a study of women with protection orders in 2007, said cases of parents carrying out such threats were rare.

"You can think of any number of guys who have killed their partners. Less often have they killed their children as well," Dr Robertson said.

"The one thing that stands out is the incredible possessiveness that seems to be evident in such cases: 'I can't have her, nobody else will'."


Dr Busch said about 60 per cent of men who killed their partner or their children took their own lives.

"They always kill themselves, that's the New Zealand way," she said.

"It's really a tactic of power and control to threaten suicide."

A 1994 case in which Alan Bristol killed his three daughters and then himself led to a law change in 2005 requiring judges to assess the risk of violence before allowing access to children by any father against who family violence was alleged.

The law was repealed last year because it was seen as not distinguishing between levels of violence, and was replaced by a stronger requirement for judges to put a child's welfare first. Simon Collins