The Crime Branch-Crime Investigation Department (CBCID) of Tamil Nadu Police has arrested suspended constable Muthuraj.
Wanted in the Tuticorin custodial deaths of P Jeyaraj and his son J Bennicks, Muthuraj was arrested on late Friday.
Muthuraj was later remanded to the judicial custody till July 17.
Jeyaraj and Bennicks had been booked for not closing their mobile shop in time on June 19 by the Sathankulam police. They were sent to judicial custody and lodged in the Kovilpatti jail on June 21.
Jeyaraj died on June 22 night and Bennicks on June 23 morning in judicial custody, allegedly due to the police torture.
The Madras High Court while hearing the case had said there was prima facie evidence to register a murder case against the Sathankulam police officials.
The court also transferred the probe into the deaths of Jeyaraj and Bennicks to the CBCID to gather and protect the evidence till the case is handed over to the Central Bureau of Investigation (CBI).
It has also initiated criminal contempt cases against three police officials -- Additional Superintendent of Police Kumar, Deputy Superintendent of Police Prathapan and constable Maharajan -- for their behaviour at the Sathankulam police station in front of Kovilpatti Judicial Magistrate MS Bharathidasan who had gone for an inquiry.