While the girl’s family argued with community members, Mr. Bhuiyan, who lived near the victim and knew her well, slipped away from the crowd, cornered the girl in her home and lit her on fire.
The authorities said at least two of the 15 in custody were village leaders accused of tampering with evidence and meting out their own fines and punishments instead of reporting the crime to the police.
“I think it is a degradation in society as a whole for people to take the law into their own hands,” said Jitendra Kumar Singh, the deputy commissioner of police in Chatra.
Mr. Bhuiyan, who initially escaped through a window after he killed the girl, was captured on Saturday, Mr. Singh said.
Last month, the killing of an 8-year-old girl from a nomadic community in northern India ignited protests across the country and provoked political fallout for the government, including the resignation of two high-level officials from the governing party.