The Crime Branch of Criminal Investigation Department (CB-CID) arrested Inspector Sridhar in connection with the alleged custodial deaths of a father-son duo at a Tamil Nadu police station on Thursday.
The inspector has been charged under Section 302 of the Indian Penal Code.
The CB-CID also arrested three more policemen, Sub Inspector Balakrishnan and constables Muthuraj and Murugan.
A total of five policemen have been arrested so far in connection to the incident.
Sub Inspector Ragu Ganesh, who was under suspension, was arrested on Wednesday.
The Tamil Nadu government on Monday issued an order to transfer the case registered in Kovilpatti East Police Station to the Central Bureau of Investigation for probe.
The Madurai Bench of Madras high court on Tuesday heard the case and directed Thoothukudi Deputy Superintendent of Police (DSP) Anil Kumar and the CB-CID to take up the investigation.
Jeyaraj, 59, and his son J Bennicks, 31, were arrested on June 19 and lodged in Kovilpatti sub-jail for keeping their mobile phone shop in the Sathankulam main bazaar area open during a curfew imposed during coronavirus lockdown.
Jeyaraj and Bennicks were admitted to the Kovilpatti government hospital on June 22. While the son died on the same night, the father breathed his last on June 23 morning.
According to reports, two senior Inspectors have been suspended while departmental action is also being taken against two chief guards of the jail.