>>/13993/
>  look at the official documents linked here
It's all reports posted in the link, but not letters, most with dedicated front page.

Have no idea what an informal letter of the state department's oig would look like, and personally think it's too early to make a judgement on the veracity of above images.
Still think they're noteworthy though, even if (for above reasons, and some of those you mention) to be handled cautiously (i.e. with a question mark).