I don't see anyone putting the blame on whoever installed the gas cylinders. I doubt the bus owner did it himself. Are installers of gas cylinders trained? Do they check for leaks after installation? Do they sign off on paperwork following installation so they can be held accountable?
Obviously there is no, or very little, maintenance done following installation.
I can almost forgive the driver for running away at the sight of the bus entirely engulfed in flames. The gas must have completely filled the bus and virtually exploded setting everything and everyone alight. The best fire extinguisher available would not have had any noticeable effect in extinguishing the fire.
Perhaps start with enforcing all these buses must run on diesel instead of gas.