Those Sensitive U.S.-Chad Relations

Reading about the U.S. abandoning their embassy in Chad, I came across this:

The four who remain -- Ambassador Louis Nigro, a defense attache, political counselor and security officer -- shredded and burned sensitive documents and removed the flag from the compound on Saturday before heading to the airport where they are now based, officials said.

What in the world could those sensitive documents be? Have we been secretly funding some evil Chadian program? Is this where we send our prisoners to be tortured? Is it financial? I guess I'm just really perplexed. Would anyone care to make wild speculations on what is sensitive between the United States and Chad