It's the six people that's really got my spidey senses tingling. From your article:
"A passenger was able to pull Valdez off the victim and push her to the ground, where she remained until police arrived."
A burly man or two could probably restrain a woman with a knife (they might get wounded in the process, but they'd probably be able to do it). For this person to have stabbed six without anyone being able to intervene...