I wrote my law dissertation on this case!
There's lots of subtext that gets missing from most reports, but long story short they probably lied and it's unconvincing that the dead kid actually grew weaker much faster than the others. Custom of the sea was you were supposed to draw lots, they didn't, that's why they went on trial.
The trial judge was a bit of a crusader who basically forced the jury into a factual verdict, then stacked the appeal court so that the answer to the facts was 'this is murder'.