The Bureau of Investigation, predecessor to the FBI, was investigating Frank Lloyd Wright in the early 1900s. Records recently added to Footnote.com show that B of I officials wanted to "throw a scare into him". You can find the original records in the Bureau of Investigation Case Files at http://www.footnote.com/spotlight/11/the-investigations-of-fra.
These records are an excellent example of the information found in the Bureau of Investigation Case Files. The governmental agency investigated hundreds of thousands of Americans, famous and not so famous people alike. In fact, most of these were investigations of private citizens, often conducted without their knowledge.
The records usually contain detailed information of interest to genealogists: dates and places of birth, names of parents, siblings, spouses and children as well as information about professional and fraternal organizations and more. You may find information about your ancestors or other relatives in these valuable records.
You can find more at http://www.footnote.com.