Me, I see the only case nnpc has to answer is why they committed to 20%, took only 7.4% and bailed.
As a lawyer and with my crude maths, let me extrapolate. The total share available for subscription in the refinery is in the region of $13.5bn. NNPC promised to take 20% of that with about $2.7bn. Instead they did about $1bn only, which amounts to 37% of the $2.7bn they committed to. While I may wish that they took up a more prominent position in such a critical economic infrastructure, you will find, if you crank your calculators without the obvious confirmation bias that 7.4% of total shares of about $13.5bn is around $1bn. As for why they decided to withdraw, it might be they ran of financial steam or the investment wasn't all it's cut out to be. Personally, I'm relieved that another humongous sum has not gone missing under our noses in opaque circumstances.