Goldman Sachs Employee Fatally Shot on Manhattan Subway in Unprovoked Attack

"The assailant fled up to the street and has not been caught, the police said. He was described as a dark-skinned man, heavyset with a beard, wearing a dark sweatshirt, an orange T-shirt, gray sweatpants and white sneakers."

In one of the most heavily policed areas in the world (Manhattan) how was the shooter able to get away.