Yes, mistakes are made and it is tragic.
However, that is no reason to forbid police officers from carying guns. They need them, simply because there are criminals who are willing to kill people and need to be stopped.
It's an airport, they have guns at every airport in the world for security reasons. I don't see anything wrong with that.
And let the police use knifes? Are you serious? Should we bring swords and axes back also? It is much safer for a police officer to grab a gun, then a knife.
No one likes guns, but they are a necessary evil.