While Balamurugan was arrested on Sunday, the other three were arrested late on Monday evening. Police are also browsing the mobile phone videos of the incident to identify other people who was part of the mob that assaulted the duo.

The incident happened when a man mistook the north Indian workers for child lifters and raised alarm, leading to a mob gathering and thrashing the duo, leaving them badly injured.

Police identified the victims as B Gopal Sahu (25) and K Binoth Vihari (22). Police said Sahu, a construction worker engaged in Metro Rail work, had stopped a four-year-old Avinash, son of Vadivel Eswaran and Varalakshmi couple of Teynampet, as the boy crossing the road alone. This has led people suspecting him and his co-workers to be child lifters.

Issuing strict warning against spreading rumours about child kidnapping, T Nagar Deputy Commissioner P Aravindan on Monday said the public should approach the police if they notice any suspicious persons in their locality.