Commander saw, told him off but nothing done
And this was his failing. I will not accept a "I already told him" reason. It was his responsibility as section comdr (i presume?) to make the trooper put his shirt back on the moment he saw it. Not 1 second later.
Based on what I have read so far, the "failure" is with the guard comdr or 2ic (as mentioned in a previous post, whoever was on shift manning the desk at that timing CPL Dave was supposed to have surrendered his ammo and weapon at the guard room after his shift). It would be unfair for the BOS or DO to take the rap because although they are overall responsible for everything that happens in the camp during their duty, they are ultimately not at the guard room at all hours, and neither can their spot checks be made every single minute.
To put it in another context, if the BOS or DO did a spot check and found the ammo/weapon/personnel missing, they would not be in the wrong would they? They surely would be in alot of sh*t to help with the investigation and drafting of the initial reports, but I would figure that would be just about it.
Do not be too quick to witchhunt superiors. If they have carried out their duties as per SOP, they would not be in any trouble. Realistically there is no such thing as zero incident. It is how you manage it. If the BOS and DO failed to report on the missing personnel, then that is their failing. Which is not the case here.
In this case, the guard comdr/2ic has failed in one or more of his procedural duties and therefore should be punished accordingly.
If one were to "Oh, all the superiors are responsible". Then in this case you would have to ask the president to resign immediately. As he is the supreme commander of the armed forces.
It is just my viewpoint that the "chasing of who's at fault" in this case ends at the guard comdr/2ic. Of course, my friends you are all free to disagree with me
add-on: Oh, and also deciding if the sentry is "not vigilant" would also hinge on whether he is actually able to see the point at which CPL Dave escaped from. I am not familiar with the layout of Mandai Hill Camp, thus I cannot comment on this. But if from the sentry post, there is an unrestricted field of view that includes the bunk and the carpark, then the sentry is in hot soup too.