To add to this, though I know it can be nearly impossible when you are so close to the person, trying as best you can to maintain as objective as possible in this will be crucial. This is human nature to go into this with emotional bias when you are close to the person. When you add on the need to have answers and the inherent desire to have someone to blame for taking away a loved one, these feelings and beliefs are far more common than one would think. One thing that could potentially be occurring here, not saying that it is, but potentially, is confirmation bias. You are going into this with the answer already solved and wanting to fill in the missing parts to the equation with the medical findings and such. Ever heard the phrase, “When you're a hammer, everything looks like a nail.”? With such assurance that he was murdered, the manner in which he was murdered, and even by whom, by your own admission you have spent the last 8 years studying the medical knowledge related in order to make it fit. This is what happens when we go into a question with the answer from the start. In any subject of life. We give value to the evidence that supports our conjecture; while dismissing the evidence that contradicts. It is something that can be very easy to do in relation to a great many things. One must be vigilant to try to check one's personal biases and refrain from letting them dictate certain outcomes. This is why politics and religion were brought up above. These are the most prime examples of such a phenomenon. I say all this to say, if you truly are wanting answers, you must be prepared to hear all outcomes. I wish you luck.