The Pentagon has now given a more detailed account of the attack on U.S. and Nigerien troops three weeks ago, but there are still many unanswered questions. Joint Chiefs Chairman Gen. Joseph Dunford promises that after a thorough investigation, the families, Congress, and the American people will be briefed.

Here are seven things we still don't know:

1. How long did the firefight last? According to the Pentagon, a 12-person U.S. special operations team and 30 Nigerien troops were returning to base after a routine visit to a village, when they were attacked by a force of about 50 fighters, armed with small arms and rocket-propelled grenades. The firefight was going on for about an hour before the U.S. troops called for air support. It was another hour before French mirage jets arrived, but didn't drop any bombs. Why not? Was the fighting over? Did the jets scare the enemy away? Was it only after four U.S. and five Nigerien troops were killed that the U.S. Green Berets realized they were in dire straits?

2. Why weren't there any reconnaissance drones overhead? U.S. forces aren't supposed to accompany Nigerien troops on combat missions, and the U.S. assessment was that contact with hostile forces was "unlikely." But a drone overhead watching the mission would likely have spotted the large armed group nearby, or advancing on the American forces. There was a drone operating nearby, but it was tasked to look at something else. Once the U.S. requested the drone it came. But why were there no eyes in the sky in the first place?

3. Could lives have been saved? The attack occurred in midmorning, according to the rough timeline provided by the Pentagon. The bodies of three of the four Americans killed in action were airlifted out by French helicopters that evening. Two wounded U.S. troops were evacuated earlier in the afternoon. We don't know if any of the dead succumbed to their wounds while waiting for the helicopters to arrive.

4. Why no call for backup? One of the curious things is why the U.S. troops waited an hour to call for close air support. Dunford's theory is that they thought they had the situation under control, and didn't need backup.

5. Who were the attackers? The U.S. believes the group that carried out the ambush was "affiliated" with the Islamic State. But Pentagon officials caution there are a lot of different militant factions in Niger, and some are adopting the ISIS "brand," but have no direct links to the terrorist groups. There has been no formal claim of responsibility. Al Qaeda and Boko Haram also operate in that part of Niger.

6. Were they tipped off? An early report from Pentagon officials suggested the U.S. and Nigerien forces were deliberately delayed, a possible sign that some villagers knew an attack was coming. Were the U.S. troops betrayed by some of the villagers they were attempting to build a relationship with?

7. What happened to Sgt. La David Johnson? We know Johnson was separated from his unit in the heat of combat, but we don't know how he died. His body was recovered two days later by Nigerien troops. His widow was discouraged from opening the casket to see his remains, an indication of how seriously he was wounded. Was he killed immediately? Did he succumb to his wounds hours later? Was he captured and killed by the enemy? Dunford has promised the family will be told the truth.