On a cursory reading of Wikipedia the obvious interpretation is that Knox and Sollecito are innocent and Guede is guilty. I didn't go through all the sites so I don't know if this would qualify as a litmus test, and assigning probabilities in this state of knowledge would be extra work.

EDIT: Read comments and am surprised at how many estimates of "Knox and Sollecito probably didn't do it" have probabilities in the range of 40% attached that they did. If it were a binary judgment or a confidence interval, then yes we should avoid extreme probabilities and widen intervals to compensate for known overconfidence biases. But in this case the hypothesis space of equally plausible possibilities is large, and some low-probability symbols were used to write the message (multi-person rape-murder vs. single-person rape-murder, female rape-murder vs. male rape-murder). It may not always be easy to unravel crime scenes (though this one sounds pretty straightforward) but to focus on Knox or Sollecito seems like privileging the hypothesis.

Unless there's major prosecutorial evidence not in Wikipedia, then this seems like a case of paying too much attention to other people's opinions (the jury, in a case where we have further information that the verdict gained media attention as possibly inaccurate), and I would suggest that anyone who gave a probability higher than .15 be more arrogant in the future.

If, of course, I just haven't done enough reading, then ignore the above.