SAN ANTONIO - A day of fun turned into tragedy back on April 18, 1999.
Mary Bea Perez, 9, was at Market Square with her family celebrating Fiesta when she disappeared.
"It's never going to go away, because, every year Fiesta comes, we remember my daughter," said Patricia Guerrero, Mary Bea's mother.
Over a week later, her body was found along Alazan Creek.
"I just tell parents, 'I never thought it would happen to me. You never know. Take care of your children,'" Guerrero said.
Her death was ruled a homicide, but police could not find her killer.
Who killed Mary Bea Perez?
Nine months after Perez's death, another shocking crime would happen more than 150 miles west of San Antonio in Del Rio, Texas.
Kaylene Jo "Katy" Harris, 13, and her 10-year-old friend, Krystal Surles, were attacked in Harris' bedroom.
Surles would run for help with a severed trachea, but Harris died from her stab wounds.
Surles was able to give police a description of a man who attacked them.
Days later, Tommy Lynn Sells was arrested.
Police would soon find out that Sells had been committing murders for years across the country.
He would later confess to the kidnapping and murder of Mary Bea Perez.
Sells was given the death penalty for Harris' murder and a life sentence for the murder of Perez in 2003.
Police have been able to connect Sells to at least 20 murders, but it's believed he could have committed up to 70.
Mary Bea Perez Remembered
It's been 20 years since her death, and every year Perez's family remember her with a balloon release at the location her body was found.
The last time we spoke to the family was five years ago on the 15th anniversary.
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