DIANE SAWYER'S EXCLUSIVE INTERVIEW WITH MARY KATHERINE SMART, WHO DISCUSSES, FOR THE FIRST TIME, HER SISTER ELIZABETH'S ABDUCTION AND HER CRITICAL ROLE IN BRINGING ELIZABETH HOME

Also: "Primetime" Meets Children Who Have Witnessed Horrific Crimes and Explores Their Heroic Actions and Incredible Resilience, Thursday, July 21 on ABC

In a remarkable hour-long report, "Brave Hearts," "Primetime" meets some courageous children who witnessed, were victims of and helped solve truly horrific crimes committed by adults against them or their family members. How, at such a young age, did they have the wisdom to be effective eyewitnesses and the strength to stay cool under pressure? And what enables them to overcome what they've experienced and just be kids again? Diane Sawyer interviews Mary Katherine Smart, who speaks for the first time about her sister Elizabeth's abduction from their Salt Lake City, UT, bedroom. The country was transfixed by Elizabeth's story and her joyous reunion with her family. Now Mary Katherine, the only person who witnessed what happened that night, describes what she saw. It was her astonishingly awakened memory that helped break open the case and bring home the sister she loves so dearly. "Primetime" airs THURSDAY, JULY 21 (10:00-11:00 p.m., ET) on ABC.

Also: Chris Cuomo meets an inspiring San Jose, CA, girl who used to watch crime shows on television, but then, at just nine years old, became a target herself. Jeanette Tamayo was kidnapped from her home and held captive by a man who severely abused and threatened to kill her. But this brave and clever girl refused to be a victim. She explains to Cuomo how, with her life literally on the line, she used techniques she learned on those TV programs to save herself and almost single-handedly put her tormentor in prison.

And: Courtney Sharon experienced something unthinkable. Cynthia McFadden reports that the way Courtney has persevered is nothing short of heroic. Late one night three years ago, a family friend made his way into Courtney's Warsaw, KY, home after asking her mother to use the phone. Police now believe the man was coming off a drug binge, out of control and looking for money. He brutally stabbed Courtney, her mother and two younger siblings. Somehow Courtney found the courage and presence of mind to play dead and then run for help. Police say her quick thinking saved her mother's life and her own, and that she had "remarkable recall" in her ability to help with key descriptions of the attacker. Her bravery continued when she later testified at the attacker's trial. Out of hundreds of children he has dealt with in interviews and investigations, "Courtney has to fit at the very top," says Detective Todd Harwood of the Kentucky State police.

Plus: "Primetime" puts some children and their parents to the test to compare how kids and adults fare as eyewitnesses. Experts explain to John Quiqones why kids can sometimes be much more accurate in their recollection than adults, and also why both kids and adults can think they remember things they never actually saw.

DIANE SAWYER, CHRIS CUOMO, CYNTHIA McFADDEN and JOHN QUIQONES are the anchors of "Primetime," DAVID SLOAN is the executive producer.