According to federal prosecutors in the James Wolfe case, the FBI “promptly opened an investigation” into the leaks after @nakashimae’s article on April 11th.
Given the security measures designed to protect the sensitive nature of the FISA, the pool of potential suspected leakers was small.
The FBI learned that Wolfe had been involved in the logistical process for transporting the FISA materials from the DOJ for review at the SSCI.