Why Did the Police Wait to Enter the School?

I took an hour and 20 minutes for the police to go in and save those kids, those kids would still be alive if the police would have immediately went in the school and get the gun man, I will never understand why the police stood outside the school for over an hour, hearing the gun shots. in my opinion I think the police were scared for their own lives, the police did want to die that's why they did go in the school, what is your opinion? I would like to state, I think me as a civilian, would have went in that school and save those kids lives or die trying. I'm just so sad about that 😞