They were the nice older couple next door. Then the first body turned up.

For Iranians, home is synonymous with sanctuary, and elderly parents, especially mothers, are revered as saint-like figures. And so they have reacted with bafflement and then outrage to every twist and turn of the case, and to the parents’ behavior -after their arrests.

Photographs in Iranian media have shown Mr. Khorramdin clad in prison pajamas flashing a victory sign. He told the authorities that he would do it all over again — and might even kill his other two adult children, too, if he were released, according to news reports.

The couple were arrested after sanitation workers collecting trash discovered a bag containing body parts on May 15. The discovery was made at a vast, well-known apartment complex called Shahrak Ekbatan, where Babak Khorramdin, a relatively unknown film director, lived with his parents. Forensic experts got fingerprints from a piece of hand, and identified him as the victim, the authorities say.