The girl's body was found in a sugarcane field after she went out to graze a herd of goats yesterday, Superintendent of Police Hari Prasath said.
"A named FIR was registered by girl's mother Poonam Devi and we arrested the accused. The arrested person's relatives and other people of his village blocked the roads in Bagaha seeking his release this morning," he said.
Bagaha Sub-divisional Police Officer Lalit Mohan Sharma said, "The girl's mother had named the accused who happens to be her brother-in-law, but later retracted when he was arrested. We are investigating the case.