I think any normal family would want to know what happened
I'm sure they would.
Remember, it's military, and the military don't always give out as much information as people want.
Also, if they did a Post Mortem Examination (Americans say 'autopsy' which sounds very old-fashioned in English), at all, it would not necessarily have been a civilian one.
Progressive emaciation, it could also be some kind of parasite.
Very possible. In hot countries there are all sorts of illnesses we don't think about in Europe.
poisoned by the locals
If that's the case, I'm sure it wouldn't be in the public domain.