'20/20' REPORTS ON HOW A SUSPECT'S GIRLFRIEND WENT UNDERCOVER TO CRACK OPEN THE CASE OF MISSING UNIVERSITY OF ILLINOIS SCHOLAR, YINGYING ZHANG

'20/20' Airs Friday, Nov. 15 (9:00 - 11:00 p.m. EST), on ABC

In June 2017, University of Illinois scholar Yingying Zhang vanished on her way to sign a lease for a new apartment and was never seen again. "20/20" unravels the mysterious case including the disturbing role Brendt Christensen, a university teaching assistant and physics PhD candidate, played in Yingying's disappearance. "20/20" reveals how his girlfriend worked with the FBI to go undercover and secretly record a confession that ultimately cracked the case wide open. The two-hour program features surveillance footage of Yingying's last steps the day she vanished and exclusive interviews with Michael Christensen, Brendt's father; FBI Special Agent Anthony Manganaro, lead agent on the case; and Assistant U.S. Attorney Eugene Miller, lead prosecutor on the case.

ABC News correspondent Bob Woodruff also travels to Yingying's home in Nanping, China, for exclusive hometown interviews with her parents Ronggao Zhang and Lifeng Ye, and to Beijing, China, to speak with her fiancé Xiaolin Hou. They open up about how they first found out she disappeared; her father and fiancé's trip to Illinois to search for her shortly after she vanished; and life now, trying to come to terms with their new reality and questioning whether the tragedy could have been prevented. "20/20" airs Friday, Nov. 15 (9:00-11:00 p.m. EST), on ABC.

"20/20" is anchored by David Muir and Amy Robach. David Sloan is senior executive producer.