The Quebec agency that investigates police officers is checking into the assault of a prisoner while in the custody of Montreal police.

The attack happened at 10 p.m. Sunday inside the SPVM headquarters on Guy St. in downtown Montreal.

The BEI said police arrested two women, at 6:45 and 8 p.m., for being drunk and disorderly, and that until 8:30 p.m. everything was fine.

However at 9 p.m., police checked on the cell and spotted one woman brutally attacking the other inmate and inflicting serious injuries.

The victim was taken to hospital and is expected to make a full recovery.

BEI was notified immediately, and seven investigators arrived at 11:35 p.m. to determine what happened. They spent the night questioning officers and examining evidence.