The solution to that is pretty simple: vote not guilty, and refuse to budge. If you need any clarification, the prosecution has not done their job. In a criminal trial, you're not there to figure out what happened, you're there to judge whether it has been established beyond a reasonable doubt that the defendant is guilty.
Whether the defense or prosecution made mistakes, if you're left with a reasonable doubt that the defendant is guilty (and I personally consider it the case that inept defense can cause reasonable doubt, unless the prosecution presents an airtight case - a lot of people, including most of my lawyer friends, would disagree with me there), don't vote to convict.
