Most women killed by their partner or ex-partner in NSW had never come into contact with the police in the lead-up to their death, underscoring the difficulties of using the justice system to prevent domestic violence.

Contrary to the common assumption that police often receive several red flags before a domestic murder, a study by the NSW Bureau of Crime Statistics and Research found two thirds of victims had no contact with authorities regarding their violent partner.

Domestic violence experts say the results of the study, which analysed all 169 intimate partner homicides in NSW between 2005 and 2014, suggest many victims are still reluctant to seek help.

"It doesn't surprise me, unfortunately," said Moo Baulch, chief executive officer of Domestic Violence NSW.