Leaving the back-to-back briefings for the House and Senate Armed Services Committee, lawmakers said there are still many unanswered questions, including why it took 48 hours to recover the body of Sgt. La David Johnson, who was separated from the rest of the team, and how the attackers were tipped off to the presence of US troops.
But the briefing has for now satisfied Arizona Sen. John McCain, the powerful Armed Services chairman who blasted the Pentagon last week
for not being forthcoming about the attack and threatened to issue subpoenas if he did not get the information he was seeking.
"I am pleased at the cooperation we're getting now," McCain told reporters. "It was an excellent briefing, we got a lot of good information. It's progress and we expect more, but this is what we've been asking for."
However, McCain did express particular concern about why it took that much time to recover Johnson's body.
The Arizona senator said he was told the investigation is expected to last about 30 days, and once the Pentagon has finished with its assessment he'll decide whether to hold a public hearing on Niger.
The October 4 attack has sparked questions not just about the specifics of the ambush but also about the role US forces are playing in Africa. The US Army team that was attacked had been gathering intelligence on a terrorist leader operating in the area before it was ambushed.
US officials told CNN that the unit was not under orders to conduct a kill or capture mission on the leader, and the team was not directed to "take direct action" against enemy forces, according to a US defense official.
"I was encouraged by the testimony that on the initial assessment, there were not significant steps that could have been taken to prevent this assault," said Sen. Ted Cruz, a Texas Republican. "The detailed investigation may produce different conclusions, so I'll certainly await the results of that investigation to ascertain what exactly occurred, but I was encouraged by the initial testimony."
But the lack of drone support for the Niger mission and others like it was a significant concern to both Democrats and Republicans.
Several noted that the head of US Africa Command, Gen. Thomas Waldhauser, told Congress in testimony earlier this year that he only had 20% to 30% of his command's intelligence, surveillance and reconnaissance needs fulfilled.
"That shortfall has not changed, and the tragic outcome of this incident in my view, can be attributed to lack of support in intelligence and resources that are necessary," said Sen. Richard Blumenthal, a Connecticut Democrat.
The attack has also sparked new questions about whether the war against ISIS is moving to Africa as operations wind down in Iraq and Syria, and whether the US needs to adjust its strategy accordingly.
"The more we succeed in the Middle East, the more we're going to see snakes run to Africa," said Sen. Thom Tillis, a North Carolina Republican. "And we've got to be prepared to advise and assist the nations there that are willing to work with us."
House Armed Services chairman Mac Thornberry told reporters that he's hoping to get all the answers to what happened in Niger as quickly as possible, but he understands it's going to take time -- particularly because US investigators will need the cooperation of the French and Nigerien governments.
"You're never satisfied because there's an urgency to find out what happened," Thornberry said. "So I expressed concern about how long the investigation is taking, until one of my colleagues reminded me we don't really know all the situation from Las Vegas yet. So it's a fair point, but we need to be right about it. We need to find the answers."