I am still waiting for an answer to my question, "What law would you enact to prevent this?" If you don't have the answer then hush with the criticism.

Now if this old man was my friend, I'd sue the police department - no doubt. The cop should've applied reasonable judgement to know that his life was not in danger - the jury might even grant it. But you just can't codify in the law as the "reasonable" part is too vague. You can't have a law to stop a cop from using excessive force when he perceives his life is in danger - even if it involves a disabled person or an old man.

Unless you answer the question I posed above, I don't see you making any point other than being angry at the situation.