>> pui leung was happy. when you land, call my cell phone number. a number we saw repeatedly throughout the case. and they hung up. and a few days later, tai calls his brother and says, chi mak, i'm going to china. >> we briefed the head of navy >> we briefed the head of navy nuclear reactors, and he says the quiet electric drive can't leave the united states. you must stop it from leaving the united states. >> qed was too sensitive. it was the deciding factor that we had to make an arrest for that. >> quite honestly, there was a lot of relief because we finally hit the stage in the investigation where, ah-ha, we got him. we finally got him.