Other than this act of violence, the thing that stood out to me is the "...witness said some people didn't even seem aware of what was happening." Situational Awareness is so important, but it can be difficult. I'm amazed at how the child noticed this. Seats on the trains face front and back and many trains have mini see-thru barriers between the entrance doors and the seats. It is not the best design. In my experience the New York, Boston and Moscow trains are designed much better, with open spaces. Still, they are not ideal, especially during rush hour, and special/sporting events. I hope the police catch these guys.