on thursday we learned that the fbi has now joined the pentagon s investigation into why what was supposed to be a routine patrol ended in an ambush that killed four american soldiers in niger. including why it took nearly 48 hours to recover the body of sergeant la david johnson. joining me now is nbc news pentagon correspondent hans nichols. hans, let s pull back for a moment for those bewildered by the fact we have more than 600 troops in niger at all. why were they there? what were they doing? well, we have around 800 troops in niger, most of them are building a drone base further north in the country. you need to have drones or at least the pentagon wants to have drones, i should couch it that way, all across africa. there are about 100 that do something call train, advise and assist. here across all of africa elsewhere countries like the philippines as well is bpc, building partner capabilities, that is standing up local forces so they can do counterterrorism.