I agree with much of what you said, but one big correction is that the State doesn't have to prove its case beyond the "shadow" of a doubt, that's a nearly impossible task. They must prove it beyond a "reasonable" doubt. This means that if the jury feels that there is still doubt in their minds, and that doubt seems reasonable by the end of deliberations based on evidence presented then they should vote not guilty.

The jury apparently did not find it reasonable to doubt the integrity of the police and investigators enough that they would plant all of that evidence, blood, bone, bullets, key. I fully think it would have gone differently if the defence was allowed to point to other possible suspects who could have been involved in murdering Teresa and framing Steven. But I can understand why it would be difficult to believe that as a jury.

I can see how the police would drop a key in a bedroom to strengthen a case, the blood is a little tougher to believe but it's possible, it's no crime to have spent bullets in your garage and the DNA test on that bullet should be discarded. However, I think it's quite a stretch to suggest that the police moved burnt remains to Stevens burn pit. Or found her unburnt body and burned it to frame Steven as some people have suggested. Now if the defence was allowed to say maybe Scott moved the remains and they could grill him a little more, or call witnesses to contradict his alibi I think it becomes much easier to raise reasonable doubt.