A medical examination into the death of a murdered Chasidic child has revealed that he was drugged by his killer.

According to New York officials, before Leiby Kletzky was smothered he was given a cocktail of a muscle relaxant, an anti-psychotic substance and pain medications.

Levi Aron was indicted on eight counts on Wednesday for the murder and for then dismembering the eight-year-old and leaving his body parts in different places.

Aron, a hardware shop worker, confessed to the crime initially, but then pleaded not guilty.

Detectives said they believed the boy was killed on July 12, around 24 hours after he was kidnapped while walking home from day camp.

His body was found early on the following morning. Aron claimed to police that he had taken the boy to a wedding party before he was killed, but Leiby's presence there has not been corroborated by guests.

Aron has undergone a psychiatric evaluation and his lawyers said he was hearing voices. But Brooklyn District Attorney Charles Hynes said he would fight an insanity defence.

In Florida, the Orthodox Jewish parents of a new son named him Ezriel Leiby. They chose the name after learning of Leiby's death while they were at the hospital for the birth, and said they felt a connection.

"A Jewish child had been lost just hours before our son came into this world," they said.