Kidnappers killed a 5-year-old boy by injecting him with acid after his family sought police help, Mexico City's top prosecutor said.

Assailants injected acid into the boy's heart and buried him on a hill outside the capital three days after abducting him from a street market on Oct. 26, Attorney General Miguel Mancera said.

A taxi driver unknowingly drove a kidnapper and the child from the market to a house, police said. The driver later saw the boy on a TV announcement seeking information and returned to the market to alert the boy's parents.

Five suspected kidnapers were arrested. Mancera confirmed the killing Monday.