An official report on the world’s deadliest aviation accident in a decade, seen by CNN, has answered one key question – but raised others.

The Air India airliner carrying 230 passengers and 12 crew members was on its way to the United Kingdom when it crashed into a building shortly after takeoff on June 12, killing all aboard, except for one survivor, and several people on the ground, according to authorities.

A preliminary assessment in last month’s disaster pointing to pilot action only deepened the mystery for people grieving loved ones.