I don't know the exact numbers, but in the retail trade a large proportion of theft involves the "back door" (i.e., employees).

We used a genuine surveillance video of a courthouse shooting to train people in our court building. An estranged husband went into a court and shot his wife. As he escaped, employees tried to obstruct him. Security experts recommended we not endanger our lives (after all, the guy had a gun and had already used it). They said they'll find an attacker eventually, and they don't need to increase the body count in the meantime. Of course, this is why many businesses tell their employees to cooperate - and terminate those who disobey orders.