The problem with law enforcement is that it does not realize that its job is not supposed to be easy. If it was easy, good cops could be found at McDonalds. I find the case in Florida to be profoundly disgusting but I do not believe that it is in the best interests of society to give up our privacy and, by implication, our liberty to make it easier for someone I do not know or trust to get an easier conviction. The basic premise of our legal system is that it is better for 10 guilty to go free than one innocent be convicted.
The reality is that none of the high tech forensic practices has prevented a single crime. All you do is get more convictions. That masks the problem -- we need to figure out how these monsters are created and work on that. To steal a line from Ben Franklin, any society that would trade liberty for security deserves neither security nor liberty. This country was not built by people who needed to be protected. It was built by people who trusted their neighbors. People who were not afraid of the dark. People who trusted their own ability to protect themselves.
The Internet is not a new force in society. It is merely a different mirror for us to look at ourselves. The government wants to know what you are doing because they do not trust you. Your boss wants to know what you are doing because he does not trust you, and if you are doing something that might compromise his business, legally he needs to know so he can cover it up. Your wife wants to know what you are doing on your computer at night because she doesn't trust you. Law enforcement officers want to see what you are doing because they do not trust you.
Do you see a pattern evolving here? Nobody trusts anybody any more. And governments and cops that do not trust the people are dangerous.
As you probably know by now, the search of that computer does not prove who made those searches in question. And Casey's mom has now testified that she made those searches relative to some other reason. Something to do with pets and some bad stuff they got into, I think.
While this case is strange (and it makes Casey look really bad), unfortunately I don't think the case is as open and shut as you state. Not that I am defending any of that family at this point. I see way too much about that case when watching CNN's Headline News while exercising in the morning.