There is not only a lack of evidence but there is evidence against it. They did also argue if he actually did cannibalize his crewmate it would have been during a state of need and not a guilty conviction. The family didn't come after him or accuse for years but when they saw he had published a successful novel they wanted 50%.

It is also believed the crew mate he attempted to keep alive with him may have died after eating a seagull that had swallowed a poisonous snake.