Bobbi Kristina died after being found unresponsive in her bathtub last June. She was 22 years old.
The Fulton County Medical Examiner determined that a combination of drowning and drug intoxication killed her.
A toxicology report also showed she had marijuana, alcohol, "a cocaine-related substance," sedatives, anti-anxiety medications and morphine in her system at the time of her death.
"It's not a mystery to me," Brown told Roberts. "The same thing that happened to my daughter is what happened to Whitney."
Brown took some of the blame, but also pointed toward Bobbi Kristina's live-in boyfriend, Nick Gordon. He said Gordon was the only person around both Houston and Bobbi Kristina near their times of death.
Gordon, 26, is the one who found Bobbi Kristina unresponsive. He was never charged by authorities in connection with her death and has publicly denied any wrongdoing.
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"He knows what happened," Brown told Roberts. "I don't know what happened that night. But he does."
Houston had taken Gordon in to live with her and Bobbi Kristina when he was just 12 years old and going through a tough period. She never officially adopted him, but Gordon was raised in Houston's house. He and Bobbi Kristina began dating after Houston's death.
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