The brother had lodged a missing person's complaint with the police.
A man along with his four friends allegedly raped his sister and then killed her in Odisha's Kandhamal district, police said on Monday.
The incident happened in Chakapad police station area on November 3, but the man and his friends were arrested on Saturday after police cracked the case, they said.
The 25-year-old woman came to know that his brother was having an illicit relationship with his sister-in-law. She asked him to end it and threatened that otherwise she would inform others about it.
To stop her, he hatched a plan, police said.
On the day of the incident, the woman went to a nearby forest to collect Siali leaves. Her elder brother was also there with his cows.
He called his four friends to the forest, got them drunk and under the influence of alcohol, they took turns in raping her, police said.
As the woman fought back, they strangulated her, and then attacked her with an axe, killing her on the spot, said Lalit Mohan Sagar, the inspector-in-charge of Chakapad police station.
The brother also lodged a missing person's complaint with the police on November 6, he said.
The woman's decomposed body was found in the forest on November 7, and in the post-mortem examination, it was found that she was raped by multiple people and then killed, he added.
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