A preliminary investigation indicated Felipe dos Santos Lima, 18, and Paulo Ricardo Martins, 19, were either asphyxiated or poisoned Friday at the St. Andrew detention center in Sao Paulo.
Diario de Grande ABC said in a translated report there were no signs of physical violence on the bodies.
Martins and Santos Lima had been shuttled around various police detention centers this summer before being locked up at St. Andrew recently. The pair were charged with the June home-invasion robbery in which 5-year-old Brayan Yanarico Capcha, a Bolivian immigrant, was shot in the head because he was crying.
Diario de Grande ABC said investigators had not ruled out the possibility the death of the two defendants was ordered by a prison gang operating at St. Andrew in retaliation for the boy's slaying.