Who is the judge of being mentally right? Here was a 77 year old man, peaceful, but stubborn. Here was a cop that broke into his house, even if he had a court summons, its still breaking into this 77 year old man's house. So, the old man did what he did and tried to protect his hearth/home. It took someone else's actions to initiate this old man response.
On the other hand, is mental illness an excuse to ignore six court hearings and a subpoena? I'm not saying that anyone should have been shot and killed - I think it's a shame. However, the two police officers were trying to enforce the law and the orders of the court. The civilian was ignoring those laws, as well as the laws regarding the upkeep and safety of the house.
You start breaking down doors, sooner or later you're gonna get double-tapped. Lots of luck to buyer Cruz, that property is now the property of the government. I have no doubt that some friend of Carol Mosely-Brown will pick it up for $400 at a very private auction.