Is there a true crime case that you're especially obsessed with?

Most of us have at least one case that we can NOT let go. If given a time machine where we can observe the past without changing it, our first thought would be: Have to see what happened that day... that night... have to solve this now.

It might not be the first case you've read about. It might not be a case that has anything to do with you. What probably happened was that the case was wrapped in mystery, and your brain clung onto it and refused to let go until you could unwrap it. I find these cases also have another thing in common... we almost always feel like we're close to solving it. We have a very strong theory - except, it's not so strong that we're positive. And maybe we know that person X did not commit the crime, but we don't know who actually did.

What is this case for you? Why are you stuck? What are you positive you've figured out? What aspects still have you confused, even after tons of research?