Jennifer guilty (spoilers)
Although Jennifer formally beat the rap for the murder (s), it is safe to conclude that she was fully guilty as her boyfriend in the killings of Mac and Muff. She is portrayed as a camp followers of criminals, drug dealers, murderers, that is how she got her kicks. There was nothing to indicate that she would protest if that boyfriend of hers wanted to commit murder.
Whatever Bugliosi or the other defense attorneys knew of the goings on on that island, came ninety nine percent from Jennifer and since we saw that she was a bare faced liar, anything that showed her in a favorable or 'innocent' line simply could not be believed. Her boyfriend was convicted before Jennifer's trial and he did not rat her out because he fell for her manipulation and he unto his dying day, probably thought he was protecting her.
Nonetheless And the Sea Will Tell is a pretty good movie with Rachel Ward to look at running around in cut offs most of the time, so what's not to like?