and weber didn't with andrew sadek. he told us sadek made three successful undercover drug buys as a c.i., half the number he'd been told was required of him. but then he stopped. weber says sadek was warned he would soon be charged if he didn't continue. then one night, a few weeks shy of graduation, security cameras snapped these pictures of sadek walking out of his dorm at 2:00 a.m. on a thursday morning. a day and a half later, he had not come back. >> tammy sadek: we got a call from the campus at about noon on friday. >> stahl: still completely unaware of their son's work as a confidential informant, andrew's parents were soon on campus, making a public plea for his return. >> tammy sadek: we love you, and we want you... we need you to come home. >> john sadek: everything will be okay. >> stahl: there were searches, prayer vigils. and then, two months later, the worst news possible-- andrew's body was discovered in a river near the campus, his backpack weighted down with rocks, its straps tied together across his ch