Sentence:  Three years in his employment a secret agent in the Post Office Department, who obtained for him the first knowledge of the star route frauds, and placed it at his disposal before it <WSD>Acknown</WSD> to be suspected by either the public or the Government. 
Meaning of the word marked with <WSD> tags:  To acknowledge; confess (often with "of" or "on"), reveal, disclose, realize