Surprised this hasn’t been brought up yet.
3 Dead (4 if you count the shooter) and multiple injured at Gilroy, CA Garlic Festival
The festival had security to include metal detectors and armed police present. However, the shooter cut through a section of the fence to gain entry. It took the police less than a minute to engage the suspect, yet the shooter was still able to kill or injure a not-insignificant number of people.