Two possibilities. The first is this was some kind of staged event. Maybe the shooter was a patsy and someone else did the shooting or he was groomed to carry out the mission. Maybe the kids aren't dead, maybe they never existed, or maybe they all died in other circumstances. Who knows. A staged mass shooting whichever way you think it went down. So naturally the police won't want anyone finding out they were in on this hoax.

The second possibility is that the shooting was real and the police made a total farce in their response to dealing with it. Children are now dead because they failed to act. Instead of holding their hands, falling on the swords, accepting responsibility and saying 'Yes we don't deserve to wear these badges'. They're trying to cover up their own ineptitude, despite it leading to the mass murder of children, just so they can keep their jobs.

I'm not sure which one is worse.