Jan. 2, 1999, is a day that will forever haunt Kimber Biggs. It was on that fateful day that her big sister, Mikelle, disappeared forever from their Mesa, Ariz., neighborhood while waiting for the ice cream truck.
Kimber was only 9 years old when her 11-year-old sister vanished. And because she was the last person to see Mikelle alive, she would grapple with the disappearance for years, blaming herself for what happened.
If you have information that might help solve the mystery of what happened to Mikelle Biggs, please contact the Arizona Police Department on their website, http://mesaaz.gov/police/, or by phone (480) 644-2211.
"[Mikelle's] like 'Oh, I hear the ice cream man,' so she went inside and got the money and came out," Kimber told ABC News' Elizabeth Vargas. "We thought he was on the other side of the neighborhood...and we waited."
But Kimber got cold and tired of waiting, so she decided to head home for her jacket, leaving her sister alone.
"Kimber came in and [said], 'I don't think the ice cream man is coming,'" their mother, Tracy Biggs recalled. "And I was like, 'It's so close to dinner anyway, and it's time to come in. And so go get Mikelle and tell her to come in.'"
But when Kimber went back outside to look for her, Mikelle was nowhere in sight. The only signs of Mikelle that remained were her bicycle and two quarters to buy ice cream, which were strewn on the street and sidewalk. An evening that began with the tantalizing bells of an ice cream truck would end with the eerie sirens of police cars.
Mesa police immediately responded to the call, where neighbors and friends frantically searched for missing Mikelle. With no witnesses, the police launched a full-fledged investigation and explored promising leads -- questioning all ice cream truck drivers in the area to following e-mail tips.
Everyone in the household dealt differently with Mikelle's mysterious disappearance. Mikelle's three younger siblings were confused and frightened.
"I was scared to go to sleep alone for the longest time," Kimber recalled. "I didn't want to be near the window... And I wouldn't go out alone in the dark...It was scary."
The night Mikelle disappeared, her brother, Nathan was 4 years old.
"All he really understood was that bad guys took her... It was just beyond his comprehension," Tracy Biggs told ABC News of her son.
Kimber recalled a night when her parents were out searching for Mikelle and she and her siblings stayed at a friends' house. Nathan wet the bed and came crying to Kimber.
"I was trying to help him get changed and cleaned up, and he said, 'What's going on?' and I said, 'Mikelle's not safe,' and then he started crying, you know, 'Well, where's mom and dad?'"
For Kimber, being the last known person to see Mikelle alive has taken its toll.
"I blamed myself for a while," Kimber told Vargas. "I remember... I was sleeping on the living room couch one night, and my aunt came in and heard me crying. And she asked me what was wrong and I said, 'It's my fault.' And she had to comfort me. She had to convince me that it wasn't my fault."
But the kids at school didn't make it any easier on her, blaming her for her sister's disappearance.
"[They] were stupid and they'd ask, 'Well, why'd you leave her alone'? And I would just start crying at school," she told ABC News. "So it made me think, 'Well, it is my fault, because all the kids think it is.'"