Why was the police response criticized in the Columbine High School shootings in Colorado? Was the IMS used also criticized?

The killings at Columbine High School on April 20, 1999, seemed to usher in a new era in American life. Since then, we have experienced many shootings in schools, gathering places, and workplaces. While Columbine may always be remembered as the tragedy that started it all, it also taught a lesson to police departments and changed the way they respond to these kinds of horrific events.
Tragically, most of the Columbine killings occurred after the police had arrived and engaged the killers in gunfire. Police training at that time dictated that the officers secure the scene and wait for the arrival of the SWAT team instead of following the killers back into the building and putting an end to their killing. It took the SWAT team 45 minutes to arrive; by then nine more students had been killed, and a teacher bled to death before he was found.
Now, police are trained to make stopping the shooter the priority. Instead of waiting for the experts (the SWAT team), police form their own “contact team” and seek out the shooter, hoping to stop him before he has a chance to kill anyone else.
Regarding the Incident Management System (IMS), Columbine also showed local agencies that they needed to learn to coordinate their responses better. Communication was a particular problem, as agencies used different radios on different frequencies and had not trained together. In such a fluid situation, information must be gathered and disseminated quickly—that didn't happen at Columbine.
http://www.cnn.com/SPECIALS/2000/columbine.cd/Pages/Managing.the.INCIDENT.htm

https://extras.denverpost.com/news/col0923.htm

https://www.washingtontimes.com/news/2009/apr/19/police-learned-columbine/