Twenty women suspected of beating their fellow to death were arrested by police in a raid into the headquarters of a religious sect in central Japan on Monday.
Police arrested 20 women late Monday on suspicion of injury leading to Okuno's death, according to a Komoro city police official. The official refused to give his name, citing policy.
The women were aged between 15 and 80, according to Kyodo News agency. Earlier Monday, television footage showed police officers streaming into the cult's headquarters to seize documents and question sect members.
Some news reports suggested Okunu was killed as punishment for failing to carry out religious rites.
Police launched an investigation after doctors who examined Okuno's bruised body raised the alarm, Kyodo said.
Kigenkai, founded in 1970, is based on Japan's indigenous Shinto religion and sells purified water the sect claims can cure diseases. It has about 400 members in branches across Japan, according to news reports.
Residents living near the group's headquarters told public broadcaster NHK they often heard drums beating from the compound and that a bottle of purified water sold for as much as 60,000 yen (US$510; EUR358.5).
Religious cults in Japan, a largely nonreligious society, have often been linked to crimes and attacks.
A doomsday sect released nerve gas in Tokyo's subway system a decade ago, killing 12 people. That sect remains under surveillance by authorities.