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.

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

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