In order to protect the government from the potential outcome of those documents (wireless power, death-ray), the US Alien Property Custodian seized the documents where they were eventually scanned into microform by the Navy. Once it was declared there was no potential harm in these documents, they were returned to the Tesla museum. When they were received, Tesla's golden Edison medal was missing.
(Interestingly, it is noted the man who scrutinized Tesla's safe belongings was humiliated by Tesla earlier when he reduced the man's design of two 34-foot towers to two 2-foot of Tesla's own. Maybe it is not coincidence it is missing?)
The rest of the documents are mostly just rejections of requests for details or sources of materials which people thought the FBI had under confidentiality, when really Alien Property had them. There are some interesting letters such as EE students looking to reproduce his experiments, biographers requesting more information and one guy linking series of unexplained plane crashers to Tesla's death-ray.
This part in particular was probably the most exciting, leaving much of the interpretation of the censored parts to the reader:
"This individual mentioned the FBI at length in these communications, pointing out that Mr. Foxtrot had been called in on the Tesla case but was killed shortly thereafter."
"He stated that the FBI investigated this matter but their hands were tied, that there was nothing the FBI could do as they had been stopped from a higher level, that -------- the FBI Agent he dealt with, resigned and requested -------- never to discuss the matter with him again, that he had a wife and family to consider and that the last hope was Congress."
[Insert permanent marker here]
"We did have an Agent, --------- who entered on duty -------- resigned [black]. The file does not indicate that we have ever interviewed ---- on the basis of -------- allegations."
Anyway, save yourself an hour or two.
All I managed to read was an article about his "death ray" and a bit about how they were worried about some other government kidnapping him and getting his inventions or forcing him to work for them.
