Matia Ssenyonjo, 47, was found dead inside the prison infirmary on Thursday where he had spent the night receiving treatment.
Frank Baine, who is the Uganda Prisons Service public relations officer, said they are investigating the matter.
Ssenyonjo, who hailed from Kayunga village, Mukubgwe sub-country, had repeatedly complained of a stomachache and other illnesses in the days leading to his death.
Baine said the dead prisoner?s name was on a list of inmates who were supposed to appear before Masaka High Court during an ongoing criminal session.
Some prison warders suspect that he was poisoned, but Baine declined to comment over the claims, saying it may jeopardise investigations.
His body was taken to Masaka Hospital for a post-mortem examination.
Ssenyonjo had been on remand since 2011 over alleged involvement in the murder of an unidentified woman in Mukungwe.
His death brings to two the number of inmates who have died in custody since last year when a key cannibalism suspect hanged himself in a cell at Masaka Police Station.
Davis Buyondo, The New Vision
