Mexico City prosecutors are investigating a video that shows officers punching and slapping three suspects while interrogating them at a store.
The tape posted on social media sites is the latest example of police and military brutality to have surfaced in recent months.
The uniformed officers appear to belong to an auxiliary police force often detailed to guard banks and stores.
In the video the three appear to be handcuffed or bound. Officers punch them in the belly or give them open-handed slaps on the ears as they question them.
The city prosecutors' office said Saturday it had opened an investigation for torture in the case and was trying to identify the officers.
Last week, a video surfaced of two soldiers and a federal police officer torturing a female suspect.