20/20 Full Episodes
20/20 RECENT REPORTS
The teen vanished on a high school graduation trip to Aruba nearly 15 years ago.
In 2017, Brendt Christensen was interrogated by the FBI in Champaign, Illinois.
"I'm angry that it could've been prevented," Mike Christensen said.
Zhang's family visits her memorial during the trial for her murder, two years after her disappearance. Xiaolin Hou, Zhang's boyfriend, said "The only way to find some relief ... is to find her."