The man behind the deadliest mass shooting in U.S. history appeared to support multiple different and sometimes contrasting extremist groups, according to the FBI, complicating the understanding of Omar Mateen’s motivation.

Mateen told a 911 operator while holed up in an Orlando, Fla., nightclub that he was aligned with Abu Bakr al Baghdadi, the head of the Islamic State in Iraq and Syria (ISIS).

{mosads}But he also expressed support for the Boston marathon bombers and an American who blew himself up in Syria on behalf of a separate extremist group, the Nusra Front, which is linked to al Qaeda, FBI Director James Comey told reporters on Monday.

During a previous investigation, the FBI also discovered that he had allegedly boasted about having connections to al Qaeda and Hezbollah, a militant Shiite group that has been at odds with al Qaeda’s Sunni branch of Islam. That investigation was closed in 2014, when officials determined there was not enough evidence to prompt a charge in the case.

The evocation of multiple extremists paints a complicated picture for the FBI, which is continuing to investigate why Mateen killed 49 people in Pulse, a gay nightclub, early on Sunday morning.

“I don’t know what to make of it, except that it underscores the importance of the work we’re now doing to find and understand all of his motivations and, if there are multiple, what they are and how to untangle them,” Comey said during a briefing at the FBI’s headquarters in Washington.

“We will continue to look forward in this investigation — and backward,” Comey added. “We will leave no stone unturned. And we will work all day and all night to understand the path to that terrible act.”

Mateen’s killings are being investigated as an act of terrorism, but Comey and other administration officials have claimed that they do not believe it was directed by a foreign terrorism group or that he was part of a network operating in the U.S.