A woman survives being thrown onto the tracks during a vicious attack in the SEPTA subway.

We want to warn you that the video above may be difficult to watch.

Raw Video of Subway Attack

The attacker and the woman were alone at the SEPTA subway station at 8th and Race in Chinatown on Tuesday afternoon. He asked to borrow a light for his cigarette. Then, without warning, he attacks her, drags her onto the landing and throws her down onto the tracks.

SEPTA Chief of Police Thomas Nestel tells NBC10 the woman, 23, was very fortunate she walked away with only bumps, bruises and some cuts.

"It's horrifying. And when you see that happen, you think the worst. We all know that there is a tremendous electric source. You touch that, you die," Nestel said.

Why then, didn't SEPTA get the attack video and the man's description out to the public as soon as possible?

Nestel says he made the call not to go public because the attacker had a very distinct jacket on and he was confident that was their best lead.

He admits it was risky, but "it's also risky to put that information out. He gets rid of that coat and I lose my best chance to get a dangerous man off the streets."

The attacker was found two days later at 15th and JFK -- in that very jacket -- by a SEPTA officer.

Police say he had the victim's cell phone on him.

Chief Nestel tweeted this praise for the arresting officer:

William Clark, pictured below, faces assault and robbery charges.