The incident happened when the suspect was being interrogated at the Navua police station earlier this week, where the victim sustained serious burns to much of their body.
On Tuesday, the police in a statement said three constables had been charged with one count each of commiting an act intended to cause grievous harm.
Benedito Bolabiu, Laisenia Naiwau, and Lasaro Turagadrau appeared in court on Wednesday, where they were granted bail.
The police said further charges were being considered.