How far should the police be allowed to go?

There is a high-profile case going on in my state right now and I would like to know what you think of it. A very large swat team went to a young guy’s house to serve a search warrant, as they suspected that he was growing pot in his basement. They came in unmarked cars, not wearing police uniforms, surrounded the house and broke down his door in the middle of the night, rushed in, and he opened fire on them. He killed one and wounded five more.

They are trying the guy for murder, attempted murder and so on. I can see a police warrant if the guy had murdered or kidnapped someone, but for growing pot in his basement? Is that so important? In my ultra-conservative state, I seem to be the only one that feels this way. What do you think?