"I was scared, but then I see the 'call help' button, but if I reacted, I didn't want him to react and attack me, because there was nobody on the train," said Jerrica Daniels.
The incident happened Sunday morning as Daniels was on her way from Union Station to Pasadena on the Gold Line. She said the suspect followed her onto the train and took a seat right across from her.
Alone in the car, she set her phone next to her on record, pretending not to notice the graphic activity suddenly taking place.
"At first I thought he was scratching himself, adjusting himself, but he kept going, and it was just like a stare. I felt him just staring at me, and I see him from the corner of my eye, and I was like, 'Oh my gosh,'" Daniels said.
The Los Angeles County Sheriff's Department's Transit Policing Division is investigating and working with Metro to review cameras on the train and platforms to identify the suspect.
Daniels posted the video to Facebook to serve as a warning to others, afraid the suspect could turn violent.
If you have any information on the suspect's identity, you're urged to contact the LASD's Transit Policing Division at (888) 950-SAFE.