Norma Hernandez, 53, said she learned from family members that her brother, Pedro, had "confessed to killing a kid" at a prayer meeting in Camden, N.J., The Wall Street Journal reported.
Hernandez said she believed her brother's admission and told Camden police about it.
It wasn't immediately clear what if anything Camden authorities did with Hernandez's information.
A spokesman for Camden police said they would see if there was any record of her claim.
Pedro Hernandez, 51, of New Jersey, was charged last week with second-degree murder in connection with Etan's death.
He was arrested after telling authorities that he lured 6-year-old Etan with the promise of a soda, strangled the boy and then dumped his body in the trash.
Hernandez is currently undergoing a psychiatric evaluation at Bellevue Hospital Center in New York.