Police say a man followed the 15-year-old girl onto a Metro bus and then began performing a lewd sex act in front of her.
The girl pulled out her cell phone and began filming the man, in hopes that the footage would help land him in jail. Police are now using the video to track the man, and they're offering a reward to anyone who can identify him.
The girl told police she was boarding route 128 at 16th Avenue when "a creepy guy" got on and sat down across the aisle.
Right away she could see that he had pulled down his pants and wanted her to look at him. Instead, she started recording the incident on her cell phone.
Regular bus riders say these types of crimes happen more often than people would think.
"Like bums on the sidewalk. I'll be walking and they'll just show me their privates," one rider said.
In this case, the man tried to talk to the girl. He first asked if she had lotion, and then he asked if he could call her later.
After a few moments, the girl stopped recording and got up to tell the bus driver about the predator on board. At that point the man jumped off the bus and ran away.
Although the cell phone recording provides key evidence in the case, police don't recommend people film predators.
"You really don't know how a person is going to act in this particular case. They could go off and start assaulting you, assaulting others. We just never really know," said Myrle Carner of Crime Stoppers of Puget Sound.
Bus riders say they take their chances riding public transit, but the system is well patrolled and seems to be getting safer all the time.
"I think they're starting to patrol it better," one rider said. "A lot better."
Crime Stoppers if offering up to $1,000 for information that helps police arrest the man.
Anyone with information about the case is asked to call the Crime Stoppers Tipline at 1 (800) 222-TIPS (8477).