Backstory: Behind the terror takedown

When a U.S. special operations team suddenly surrounded the car carrying the Islamic State's second in command, he was given the split-second option of surrendering. Instead, he began firing.

"He made a bad choice," a senior military source told Fox News.

Abd al-Rahman Mustafa al-Qaduli, also known as Abu Ala al-Afri and Haji Imam, died in a hail of bullets early Thursday morning on an isolated road in eastern Syria, a location described by U.S. military officials as being "in the middle of nowhere."

Defense Secretary Ash Carter told a press conference Friday he was ISIS' finance minister. But the terror leader also was considered the man most likely to take over for ISIS leader Abu Bakr al-Baghdadi, if he were captured or killed.

Details of the takedown emerged Friday, including descriptions of the elite U.S. assault force arriving in helicopters as drones flew overhead, tracking him.

When al-Afri refused to surrender, he and all those with him were killed. If he had been captured, he would have been interrogated and then handed over to Iraqi authorities.

The U.S. team had been practicing the mission for weeks. "It was a really good mission," one source familiar with the developments told Fox News. "It was precision and went as planned."

"We are systematically eliminating ISIL's cabinet," Carter said at the news conference.

“The removal of this ISIL leader will hamper the organization’s ability to conduct operations both inside and outside of Iraq and Syria."

Carter described the target as responsible for funding ISIS operations and involved in some external affairs and plots.

He said this was the second senior leader successfully targeted this month, in addition to the group’s “minister of war” Omar al-Shishani, or “Omar the Chechen,” killed in a recent U.S. airstrike.

A U.S. official told Fox News that the Brussels terror attack earlier this week prompted the raid in Syria.

Al-Afri is a former physics professor from Iraq who originally joined Al Qaeda in 2004. After spending time in an Iraqi prison, he was released in 2012 and traveled to Syria to join up with what is now ISIS.

On May 14, 2014, the U.S. Department of the Treasury designated him as a “Specially Designated Global Terrorist” for his role with ISIS.

The Chairman of the Joint Chiefs of Staff, Gen. Joe Dunford, also said at the press conference that more U.S. troops might be headed to Iraq soon.

"The secretary and I both believe that there will be an increase to the U.S. forces in Iraq in the coming weeks,” Dunford said. “But that decision hasn't been made."

He added that despite a number of high profile strikes against the terrorists, by no means would I say that we're about to break the back of ISIL or that the fight is over."

Fox News’ Lucas Tomlinson and Jennifer Griffin contributed to this report.