Through much of 2016, some US intelligence suggested Baghdadi was likely alive and hiding somewhere west of Mosul, Iraq, but now the US doesn't have a sense of where he is or if he's even alive according to a senior US official familiar with the intelligence.
In December 2016, a US official told CNN that the US had "been aware of some of Baghdadi's movements".
At the time, the official had access to some of the most recent US government reporting on ISIS, but because of the extreme sensitivity of the information, they declined to offer more details, including whether their intelligence indicated if Baghdadi was in Syria or Iraq, or to what extent he was hiding.
But now US officials say they don't know if he is dead or alive. On Tuesday, the top US commander in the fight against ISIS, Lt. General Stephen Townsend told reporters, "I don't have a reason to believe that he's alive. I don't have proof of life, you know."
While US officials have long said the fate of Baghdadi would not change the war against ISIS, his status is a matter of media fascination, especially after the fall of Mosul -- where he declared ISIS' called caliphate in 2014.
In recent months there have been numerous unverified reports circulating that the terrorist leader has been killed.
Last month, the Russian Defense Ministry said it was investigating reports that Baghdadi was killed in a May airstrike in Syria which struck dozens of ISIS operatives holding a meeting. Overhead imagery of the airstrike location was also released.
While it was considered doubtful by the US that Baghdadi would take the risk to his personal security of appearing before a large number of people, CNN has learned US intelligence did scrutinize all available information to see if there was any truth to Russia's claim and concluded he was not at that location.
Townsend gave a hint that the US had been working to determine if the Russian reports were accurate: "The Russians some weeks ago claim to have killed him in an airstrike. ... I've received some reporting since then that suggested he was not killed there by the Russians."
There have also been no announcements from ISIS and no communications have been intercepted indicating he is dead.
So Baghdadi's current fate is a mystery as Townsend made clear: "Quite honestly, don't know. I hope he's deader than a door nail. If he's not, as soon as we find out where he is, he will be."
But Townsend did offer his thinking about what it might mean if Baghdadi has been killed. "If he is dead, that means someone's running ISIS. And I think that they're trying to keep it -- his death quiet for their own morale."