The Syrian site, which was bombed by Israel in September, 2007, originally had structures that indicated a nuclear research facility was under construction. After the bombing, the Syrians promptly removed the structures, both the ones that were bombed and those left intact. Syria has since rebuilt the area with what appears to be a missile control and launching center.
UN inspectors found, before Syria rebuilt the area, that there were traces of uranium and graphite, indicating that there was indeed a nuclear research activity, at the very least, going one. The Syrians apparently did not realize that it was difficult, nearly impossible, to clear away the microscopic evidence that nuclear research was going on there.
North Korean technicians were involved with whatever was going on there, although Syria denied any nuclear work was taking place. Denying that North Koreans were around was more difficult, as North Koreans have been seen entering and leaving this area for months. North Korea is believed to be still selling weapons, and possibly nuclear technology, to Syrian mentor Iran.