It might have had something to do with the two armed guards and the unarmed undercover officer...
There is NO excuse for what these militant cops did. They are suppose to protect and serve. The protect part means you don’t throw grenades into a playpen and you make sure the person you are actually looking for is at the location. They could have took him without risking harm to others. But that would have taken effort and would have kept them from playing with their toys.