Murder accused Senthil of Keerathurai died after he clashed with Senthil Kumar, who had committed patricide, late last night, police said.
The duo had been diagnosed with mental illness and depression and were lodged in the same cell, police added.
The DIG of prison Kanagaraj and Superintendent of Police Urmila inspected the cell and suggested that Senthil Kumar be admitted to the psychiatric ward at Keezhpakkam Hospital here.
An investigation is on to ascertain why both the patients were lodged in the same cell, police said.