Rajesh Talwar, father of murdered teenager Aarushi Talwar, was on Tuesday attacked outside a special Central Bureau of Investigation (CBI) court.
Mr Talwar could be seen holding his head in pain as blood flowed out.
A sharp-edged cleaver was seen on the ground as television cameras caught details of the assault and security personnel grabbed a young man who had attacked him.
Aarushi, 14, was found murdered under mysterious circumstances in her parents' Jalvayu Vihar apartment in Noida, May 16, 2008. Their domestic help Hemraj was initially suspected for the killing, but his body was found on the flat's terrace a day later.
Mr Rajesh Talwar was arrested soon after the murders but let off when investigators could not find evidence to nail him.