The tragic history of police responding too late to active shooters

Guests arrive at the joint funeral service for Irma Garcia and her husband, Joe Garcia, at Sacred Heart Catholic Church in Uvalde, Texas, on Wednesday. Schoolteacher Irma Garcia died in the May 24 school shooting in Uvalde, and her husband died two days later of a heart attack. (Eric Gay/AP)

Confusion, chaos and wrong information appear to have contributed to law enforcement's delay in stopping the gunman at Robb Elementary School in Uvalde, Texas.

The gunman spent more than an hour inside the school while police waited outside, authorities say. This was because the incident commander, school district police chief Pete Arredondo, treated the scene as a barricaded-person situation rather than as an active shooter situation.