the exact circumstances of how he became separated from his unit. the entire team, led by green berets, has been interviewed about when they last saw johnson. the u.s. team had stopped in a town on the niger/mali border to pick up supplies, including food and water and then they met with village elders. investigators believe the ambush may have begun when the u.s. soldiers were back in their vehicles, possibly even driving. as those killed are laid to rest, defense secretary james mattis on capitol hill briefed senator john mccain one day after he threatened subpoenas if the pentagon doesn't start telling congress what it knows. >> i felt that we were not getting a sufficient amount of information, and we are clearing a lot of that up now.