Asifa Bano, who was kidnapped, gang raped and murdered in the Kathua district of Jammu and Kashmir this month.
Suspect Uttam Sahu, 24, is accused of luring the child away from the party in the Indian district of Kabirdham in Chhattisgarh late on Wednesday night.
After promising to get her a cold drink, he took her 1.5km away near to a dark and deserted spot near a stream, it is claimed.
There he raped her and bludgeoned her to death with a cement brick before abandoning her half-naked body, police say.
An investigator said he didn't bother covering his tracks, returning to the wedding and partying as if nothing had happened with her blood fresh on his shirt.
'He left her body with hardly any clothes on and returned to the wedding. He had no clue that he had bloodstains on his shirt,' said Kawardha SP Lal Umed Singh.
Protests in cities across India have been held this month, with demonstrators demanding action against rapists and violence against women.
Comment: India: National uproar leads to approval of the death penalty for rape of children under 12
The rallies came after eight-year-old schoolgirl Asifa Bano was kidnapped, gang raped and murdered in the Kathua district of Jammu and Kashmir.
Days later another girl, also eight years old, was found raped and murdered after being kidnapped from a wedding in Etah, Uttar Pradesh state.
In this latest case, witnesses told police the suspect 'had his eyes on [the girl] all evening', The Times of India reported.
The girl's family reportedly began looking for her after the attacker returned to the wedding. Guests told them they had last seen her with Sahu, a friend of the groom.
They found him with bloodstains on his clothes and called the police. Officers found the girl's body the following morning.
Sahu has been charged with rape and murder.
R.C. asks, doth supra seem seem familiar? If not, mend your learning. If so, (and despite tragedy), enjoy: Interesting confluence of names, or rANO and bANquO eh? Sad, though.
R.C.