Amnesty International says Papua New Guinea police must launch an immediate and thorough investigation into the death of human rights activist, Anna Benny.
Ms Benny, who worked with the group Meri I Kirup Sapotim, disappeared in November last year in the Highlands, after she went to help her sister-in-law who was accused of using sorcery.
Both women were killed but there has never been a police investigation.
A spokesperson for Meri I Kirup Sapotim, who has asked that her name not be revealed, says there are increasing numbers of people being accused of sorcery and killed.
"We hear stories all the time and we know that it has happened but the police continue to say that someone has to file an official complaint, but no one wants to file an official complaint because they fear for their lives."
Amnesty Interational says police must also work with other agencies to challenge views which contribute to violence against women and girls.