S Vijayan, the policeman attached to Pudupet Armed Reserve, who was attacked by a gang earlier this week in St Thomas Mount, succumbed to injuries on Thursday.
Police have arrested four people identified as Ajithkumar, Vinodkumar, Ravi and Vivek.
Vijayan had tried to intervene in a quarrel where one of his friend was involved when he was attacked on Monday night.
Ajithkumar later fractured a leg while trying to escape from police. On Wednesday, police said, Vijayan, 32, was at the Pazhavanthangal market with his brother-in-law Vasudevan when the latter’s friend Ajmal called him and said he was being attacked by a gang at Alandur Kannan Colony ground.
A seriously-injured Vijayan was then rushed to hospital where he died on Thursday night.
Police had tracked the accused with the help of CCTV footage on Thursday.