Mysterious Korean 'ghost ships' found in Japan: What we know

 Tests are being carried out on decomposed bodies found aboard so-called "ghost ships" that have entered Japanese waters in the past five weeks.

The key questions facing authorities: Who are they? And where

did they come from?

Evidence found on the boats and their grim cargo suggest they came from North Korea. But are they attempted defectors or fishermen who've strayed too far from land?

Here's what we know so far.