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b'The fate of little Isabel Celis was unknown for 5 years after the 6-year-old disappeared from her bed in Tucson -- until her remains were found in a desert grave last year. With the arrest of a convicted sex offender, the family know has more answers. The family of another murdered Tuscon girl - Maribel Gonzales -- also knows what happened to the 13-year-old in 2014.\\xa0Christopher Matthew Clements, 36, is charged with killing both. Nancy Grace looks at how the system may have failed as the suspect was allowed to walk free despite a long rap sheet of crimes. Her experts in this episode include\\xa0Marc Klaas -- founder of Klass Kids Foundation, psychologist\\xa0Caryn Stark,\\xa0forensics expert\\xa0Joseph Scott Morgan,\\xa0\\xa0juvenile judge & lawyer\\xa0Ashley Willcott,\\xa0and\\xa0CrimeOnline.com reporter\\xa0Jennifer Dzikowski.'