This type of failure is extremely rare but the investigators not only need to find the chain of events which likely caused it but also the following chain of events which caused a lot of fuel to leak out from somewhere, probably onto the ground where it then started to vaporise and subsequently ignited.
With all the videos and other evidence they collect from various sources it may be possible to determine where the fuel exited the aircraft and where the first ignition took place. All this is amongst the myriads of things they will have to look at before trying to determine what steps may need to be taken to minimise the chances of it happening again. These processes could take days, weeks or months, or longer. Then of course there will have to be cost and safety evaluations by various parties….
It has already been mentioned by some that the seat of the fire appeared to be below and not in the aircraft and one of my thoughts is that hot brakes could have ignited it or it could have been ignited by another fire already burning in or around the engine. It may of course be difficult to tell after all the damage caused by the fire(s).