Experienced FBI investigator Peter Strzok has left the special counsel team and joined the bureau's human resources division, ABC News reports. It is unclear why Strzok decided to leave Mueller's probe.
The news has been rife with stories about Mueller's expanding probe into potential ties between President Donald Trump's campaign and Russia, and Strzok's departure marks the only known exit among Mueller's principal team.
Mueller's probe has grown increasingly aggressive in recent weeks. The FBI raided former Trump campaign manager Paul Manafort's home last month, and it also came out that he had impaneled a grand jury in Washington, D.C.