The article goes on to quote Comey’s book and its description of this “development”:
In early 2016, the U.S. government became aware of information from a classified source, and “the source and content of that material remains classified as I write this,” according to the book.
“Had it become public, the unverified material would undoubtedly have been used by political opponents to cast serious doubt on the attorney general’s independence in connection with the Clinton investigation,” Comey writes, without further elaboration.
Comey asserts that he didn’t sense Lynch interfered with the investigation, even after the highly publicized Phoenix tarmac meeting between Lynch and former President Bill Clinton. That episode convinced Comey that he needed to step forward with his own public accounting of the email server investigation. (emphasis added)