A fair amount already seems pretty clear. The essential cause of the disaster was the fact that the fire spread catastrophically, and this was enabled by the kind of cladding which was used, which has a relatively combustible layer at its core.

Other factors contributed - the lack of any sprinkler system, of the sort that is universal in modern offices and in private residential developments, and no doubt other things - but what shaped everything, and made things so disastrous was the rapid spread of the fire.

But the physical cause is only the start of it. What matters is to make it impossible for this to happen again, which is going to mean major building work all over the place, getting rid of fire hazards like this kind of cladding wherever it has been used. And alongside that, finding how it was allowed to happen, and how all the lessons of previous fires had been ignored. If there are scapegoats, they need to be the right ones, at the top.