Nearly three weeks after the deadly ambush on U.S. Special Ops forces in Niger, ABC News has learned chilling new details about the mission gone wrong from a survivor of the attack and a senior U.S. intelligence official.

Their accounts, provided in separate interviews, raise questions about why a second, potentially more dangerous mission was tacked on late in the day even after a second team that was supposed to join them was unable to do so.

What was started as a reconnaissance mission to meet with local leaders turned into a kill-or-capture mission aimed at a high-value target, according to both sources.

That target – codenamed Naylor Road – has ties to both al Qaeda and ISIS, according to the intelligence official.

According to multiple intelligence sources, this target is one of the U.S.’s “top three objectives in Niger,” one that the U.S. has been “actively pursuing.”

But that change in plan meant that the team was out for over 24 hours and put them at greater risk.

“They should have been up and back in a day. Because they were up there so f------ long on a mission that morphed, they were spotted, surveilled and ultimately hit,” the official said.

PHOTO: An honor guard stands at attention as a hearse carries the coffin of U.S. Army Sergeant La David Johnson, who was among four special forces soldiers killed in Niger, to a graveside service in Hollywood, Fla., Oct. 21, 2017. (Joe Skipper/Reuters) More

Despite being massively outnumbered, the American and Nigerien troops held their own -- including Sgt. La David Johnson, who was killed in the ambush, the sources told ABC News.

“He was the best kid you could ask for,” the survivor said of Johnson, who fought back the militants with machine gun fire from the back of a pickup truck, before grabbing a sniper rifle and continuing to shoot.

“The guy is a true war hero,” the survivor added. “I really want his wife and kids to know that.”

The team of 12 Americans set out with 30 Nigerien soldiers in the early morning on Oct. 3, according to the sources and confirmed by Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, who on Monday offered the first official timeline of events for the ambush in Niger.

They rode in six to eight vehicles, three of them American. They were headed from Niamey, Niger’s capital, to a village 85 kilometers to the north, called Tiloa.

Their pre-mission threat assessment never considered the possibility of 50 to 60 enemy combatants attacking them, according to the official. That matches what Dunford told reporters on Monday. He also added that the leaders on the ground assessed that contact with the enemy was unlikely.

On their way back, the team received a call from the base back in Niamey, asking them to turn around and kill or capture a high-value target who is a known al Qaeda and ISIS operative, according to two senior officials.

There was “high confidence” that the target was in the area, the sources told ABC News. A second U.S. Special Forces team was directed to meet up with their patrol, but when they could not, the original 12-member team and their Nigerien partners were told to proceed anyway.

The team arrived at the target location in the early morning hours of Oct. 4, but found nothing. They burned the remnants of the abandoned campsite and headed back south as the sun came up, stopping back through a nearby village called Tongo Tongo around 8:30 AM.

There, the Nigerien force requested they stop to eat, while U.S. soldiers met with a village elder, who was “obviously and deliberately trying to stall them,” according to the official.

“He was definitely stalling as long as he could to keep us there,” the survivor said, saying he had an entourage, showed the unit a child with an illness, and even grabbed a goat he wanted to prepare for them.

PHOTO: Members of the Special Forces cry at the tomb of Army Sgt. La David Johnson at his burial service in the Memorial Gardens East cemetery, Oct. 21, 2017 in Hollywood, Fla. Sgt. Johnson and three other U.S. soldiers were killed in an ambush in Niger. (Gaston De Carden/AFP/Getty Images) More

But the unit suspected something was definitely wrong when they saw two motorcycle riders watch them and race out of the village.

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