other sites, including yongbyon the nation's main atomic complex just 50 miles north of pyongyang. and this factory in chongsu near sue chinese border, suspected of producing nuclear material. david albright is a former weapons inspector. do you need to see weapons inspectors on the ground to believe any deal is real? >> the only way to know if north korea's representations are accurate is to verify them through on the ground presence. >> reporter: north korea granted such access as part of a clinton-era deal, but north korea kicked out the inspectors after the bush administration accused it of cheating. this time the trump administration wants to destroy the weapons itself with assistance from other countries. components would then be shipped to a research lab in tennessee. depending on how truthful kim jong-un is, that process could take anywhere from two to ten years. another challenge, monitoring north korea's nuclear scientists. how many people in north korea know how to build a nuclear weapon?