The investigation into the drug-smuggling mouse turned up 29 small packets of marijuana and 23 packages of cocaine.
Gomes said officers are reviewing CCTV footage in an attempt to determine who was behind the scheme.
"They attached a hook to the mouse's tail and then used it to carry the drugs and other goods from one cell to another," Gomes told G1. "When the animal arrived at its destination, the prisoner took the mouse and removed the hook from its tail."
A video shared by prison officers shows the tame mouse allowing investigators to pet it on the head.
The mouse was released outside the prison, officials said.