A man was arrested Monday night after police say a woman took a picture of the man exposing and touching himself on Metro trains.

Police believe the man they arrested was exposing himself and touching himself inappropriately in front of women while riding the Metro.

One woman ever tweeted a video of it happening to her.

Shortly after 7 p.m., police say officers stopped a man who matched the description of a person of interest in an indecent exposure incident. The woman who witnessed the incident is working with police to make a positive identification.

WUSA9's Stephanie Ramirez was there when the man was being arrested. She reported that police told the man he is accused of masturbating on a train. The man denied the accusations.

“I know I did not do that,” is what the man told Metro police when they explained to him he was accused of masturbating on a train.

The man denied it several times, but the tweets posted show a man matching the same description caught in the act. One of the photos actually shows the suspect holding himself.

The woman who took the photos said on Twitter, this all happened on the Blue Line going from Largo to L’Enfant Sunday morning and that the man had followed her and was staring at her while he exposed himself.

On Monday, the suspect arrested appeared to be wearing the same clothes and had the same book bag as the man in the tweets.

Before WUSA9 witnessed him getting arrested, people gasped watching the posts outside of L’Enfant Plaza, which got more than 16,000 shares.

A Metro Transit Police Spokesperson says they’ve made contact with the woman who took the photos and video. She told WUSA9's Stephanie Ramirez online that police were on their way to pick her up and take her to the station to identify him.