CHICAGO - It is one of Chicago's most renowned and frustrating mysteries.
Next week will mark 20 years since two young, vivacious sisters, Diamond and Tionda Bradley, vanished into thin air.
Police have spent thousands of hours pursuing hundreds of leads.
How often does their family think about the missing girls?
"All the time. Every day. 24/7. Around the clock," the family answered in unison.
FOX 32’s Dane Placko met with the family in the shadow of the buildings where the girls once played at 35th and Lake Park Avenue in the Bronzeville neighborhood.
"It's hard to go through life knowing that you have loved ones out there that you have no idea where they are," said April Jackson, the girls’ aunt.
Diamond was just three-years-old and her sister, Tionda, was 10-years-old when they disappeared on the morning of July 6, 2001.
Their mother, Tracey Bradley, told police she last saw the girls around 6:30 a.m. when she left for work. She returned home around 1 p.m. to find a note saying they had gone to play at a nearby school.
Their disappearance sparked a massive search.
Hundreds of Chicago police, federal law enforcement officers and civilian volunteers spent days checking sewers, lagoons, abandoned buildings and factories. They also interviewed nearly 100 registered sex offenders living in the area.
But 20 years later, the girls are still gone.
"To have to wait in limbo like this," said Sheliah Bradley Smith, the girls’ great aunt, "Nobody said nothing. Nobody's prosecuted. Nobody's in jail. But the girls are still gone."
P. Foster is a private investigator who's been working with the family since the girls first disappeared.
They believe there are primary suspects – one, possibly two family members – who had access to the girls the day they vanished.
"There was a planned trip for these children, to go on a camping trip," Foster said. "That camping trip is all fraudulent. That camping trip never manifested."
April Jackson says the girls had been taught to be suspicious of strangers.
"We know stranger danger. It's just embedded into our heads. So that being said, it would've had to be somebody who was very trustworthy, she really, really trusts," said Jackson.
But because there are no bodies, and the evidence is circumstantial, the family believes police and prosecutors are reluctant to file charges.
"So we're looking for that next small piece, and I do believe somebody out there has that information," said Foster.
Chicago police say the investigation remains open, telling FOX 32 in a statement:
"(Area One) detectives have and will continue to follow up when tips are received. At this juncture, there are no new leads."
A spokesperson for Cook County State’s Attorney Kim Foxx said:
"We are open to reviewing any information that is brought to us by law enforcement, who is handling the investigation of this case."
Today, Diamond and Tionda would be 23 and 30-years-old.
Angeline Hartmann of the National Center for Missing and Exploited Children said they continue to get calls and tips after releasing age-progression photos of the girls five years ago.
"Sometimes people think the longer a case goes on the less likely it is that we may find these children," Hartmann said. "But that's not the case. We've seen it over and over again. Long term missing children are found."
Hartmann points to the case of Jaycee Dugard, the 11-year-old California girl who was kidnapped in 1991, and escaped from her captors in 2009.
And in Cleveland, where Gina DeJesus and Amanda Berry were kidnapped as teens in 2003 and 2004 by Ariel Castro.
They escaped 11 years later with the help of another woman being held captive by Castro.
"We still hold out hope, yeah. Because you can't help but hope," said Shelia, the girls’ great aunt.
"This entire city is behind this family with these children," said Uncle Troy Gaston. "This entire city. We won't go away quietly."