Covering something like this up is not as easy as it sounds. Just because the local authorities are releasing the report does not mean other companies and nations are not heavily, heavily involved. Not only is the aircraft manufacturer involved, but every manufacturer of equipment on the aircraft useful to the investigation as well. Any nation with a citizen on board is likely involved as well as the FAA and NTSB. Hundreds or even thousands of people come in contact with portions of an investigation like this. If mechanical failure due to defects or poor maintenance were to blame many people would know, and many of them wouldn't work for Embraer.