The boy had lodged a complaint last Saturday, alleging that two unidentified men barged into their house in the night and raped and brutally killed his sister by strangulating her.
The incident had triggered violence between two different groups, leading to death of one person and injuries to five.
"The girl's brother confessed that he had killed his 21-year-old sister and cooked up a story of she being raped and later killed by two unidentified people," SP Shobha Bhutada said, adding that the girl was not raped.
Police also detained 15 people who were involved in the violent group clash.