The father and his relatives absconded after the young man Praveen Sahu's body was found in the Pithoria forest in Ranchi district.
The girl, Reshma Ansari, gave a dying statement to the police on Friday, saying she was raped by three youths called by her father, Moin Ansari. Sahu was brutally tortured in her presence and she had no idea if he was dead or alive.
"We have arrested the girl's maternal uncle, Rakib Ansari," AV Minz, superintendent of police, Ranchi Rural, said.
The police said they found Reshma unconscious in the forest on December 14 and rushed her to a government hospital where she recorded her statement before dying of internal and external injuries.
The police said the couple was forced into a four-wheeler and driven to Pithoria.
Reshma's statement says, "I last saw Praveen tied with a rope and dragged away in the dark. Later, on my father's order, the vehicle driver and two others pounced on me and raped me. They thought I was dead and threw me off a bridge."