‘A fundamental security failure’: How did a gunman open fire on a Trump rally?

Jillian Snider, a retired New York City police officer who was often detailed to political events, said it is routine for law enforcement to do a perimeter check extending a few hundred yards ahead of such an event.

“That doesn’t mean that someone can’t sneakily make their way to one of those positions afterward, especially if it was someone who had done some preplanning,” said Snider, an adjunct lecturer at John Jay College of Criminal Justice. “There are a lot of places in that area to hide, and you can’t monitor every possible position.”

“Someone who is that driven to do something like this will find a way to try and get the job done,” she added.