Malaysia plane search: Why terrorist attack is unlikely
29 May 2014 Last updated at 09:56 BST
Mystery still surrounds the fate of the Malaysia Airlines passenger plane that disappeared on 8 March with 239 people on board as it flew from Kuala Lumpur to Beijing.
Wreckage from flight MH370 is not in the area where four acoustic pings were heard in April, Australian officials say, after a robot submarine scanned the area.
Theories abound about what might have happened to the plane which officials believe ended its journey in the Indian Ocean, north-west of the Australian city of Perth - but experts consider a terrorist attack unlikely.
BBC News outlines why - in 60 seconds.
Video produced by Michael Hirst