Two more officers of the CBI team that probed the Tuticorin custodial death case tested positive for COVID-19 on Friday, while one of the accused policemen is found to have contracted the virus.
The CBI office cum quarters at Athikulam, where the investigation was held and four officers from Delhi were staying, has been sealed and disinfected.
While two officers tested positive for the virus on Wednesday, the others on Friday, officials said.
The police personnel arrested in connection with the case and lodged in the central prison has been placed under quarantine, they added.
The father-son duo, Jeyaraj and his son Bennicks died in a hospital in Kovilpatti in Tuticorin district, after they were allegedly thrashed by the personnel at Sathankulam police station.
The state government has transferred the case to CBI following public outrage over the incident.
The CBI has swung into action as soon as it received a reference from the Centre to proceed with its investigation and had dispatched a team from its special crime unit.
The team reached the location on July 10 and collected crucial forensic evidence and met a large number of people during the field work, possibly exposing the members to the contagious pathogen.
The father and son were arrested by Sathankulam police for alleged violation of prohibitory orders in force due to COVID-19 lockdown by keeping their mobile phone shop open in Tuticorin district beyond the allowed time.
They were taken to jail in the early hours of June 20.
While Bennicks died on June 22, his father Jeyaraj died of injuries within hours on June 23.
The ghastly manner in which the two were allegedly beaten by police personnel had evoked a sharp response from civil society, movie industry and political parties, resulting in the recommendation of the CBI probe by the state government.