Bay Area Rapid Transit police are investigating an amateur sex video that was apparently shot on a moving BART train.

Deputy Chief Ben Fairow said his officers are trying to track down the cell phone video that shows a partially disrobed couple having intercourse on a seat at the end of a BART train car.

The windows are dark, suggesting the train was in a tunnel at the time the video was shot, but the timeline and exact location were not known.

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It shows grainy images of the couple's faces, but BART has not been able to identify the people.

If they do, Fairow says the couple faces a misdemeanor charge and a system-wide ban.

“It’s not considered a serious, violent offense, but it is something that we take seriously. It’s also one of the crimes that’s eligible for an AB 716 prohibition order which is a new law that went into effect to prohibit certain individuals who commit certain offenses from being in or around our properties," Fairow said.

BART is also using the incident to call for all riders to alert them of inappropriate behavior. The agency says it tries to make sure officers are waiting at the next stop anytime illegal activity is reported on a train.

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