"The Central Bureau of Investigation (CBI) officers probing the case also tested positive on Friday, along with another accused Sub-Inspector Pauldurain," Prison Deputy Inspector General Palani informed.
Last month, P Jeyraraj (55) and his son J Benicks (31), were allegedly tortured in the police station, leading to their deaths.
Five policemen have been arrested in the case and have been transferred to the Madurai Central Jail from Thoothukudi. A district police court had earlier ordered a 15-day remand for three police officials in the case.
The father-son duo was arrested were taken into custody on June 19 and were lodged in Kovilpatti sub-jail for keeping their mobile shop open during a curfew imposed during COVID-19 lockdown.