If somebody had worked out information regarding a potential flaw in something, lets say a new super-dooper aircraft design, and declined to share this information and the aircraft crashed due to this flaw, and if it was later discovered that this individual knew the flaw could criminal charges be issued against them for doing nothing?
In other words are people libel for not sharing information that they have no official reason to share. In the above example we can assume the knowledgable individual has no connection with the aircraft but he's just a amateur observer.
Hope that makes sense.

I don't think the person who keeps quiet is guilty of anything in English law, but other legal systems might take a different view.

It would be very hard to prove that the person knew.