Subbian (65) of Pallapalayam, a watchman at a commercial complex at Pappampatti near Sulur, was found dead near a jewellery shop on Tuesday morning.
Passers-by informed the jewellery shop owner and the police.
The police said that the jewellery shop belonged to Anand of Kuniamuthur.
The shop had close to 2 kg of gold and 10 kg of silver on Monday night.
The police said that a group of persons who came in a car tried to break open the jewellery shop early on Tuesday. When Subbian saw this, he raised an alarm.
The gang beat him with an iron rod on his head causing his death.
The gang might have fled the scene when they realised that the watchman had died, the police said.
Sniffer dogs, and forensic experts have been pressed into service.
The police have formed three special teams to probe the incident.