"We had been playing on the porch, riding tricycles and crashing into each other like kids do," Martin, who was 4 at the time, said about the last time he saw his 7-year-old brother. "I remember I got mad and went inside to tell mother that Billy hit me too hard. It couldn't have been but just one or two minutes before we came back out on the porch and he was gone."
Crosley, who was 10 at the time, didn't get to see Billy that day because she was at her grandparent's home, but she hasn't forgotten the charming smile and bashful nature of her brother.
"Why should I forget family? You go on with life but you don't ever forget," she said, fighting back tears.
Both Martin and Crosley say a familiar smell, looking at an old photograph or a hearing a particular word can trigger a vivid memory from 50 years ago: The house filled with neighbors and law enforcement personnel, their parents being interviewed, seeing the faces of people who came back from search parties without anything to say to their family.
"It all just comes flooding back into your mind," Crosley said as her brother nodded in agreement. "It's forever etched in your memory, you can't forget."
The hardest part of their brother's disappearance was no form of closure for their family, especially their parents who died without ever learning what happened to their son.
"They are in heaven now, and hopefully they know the truth, but our parents were in a zombie stage at the time. Hope is the only thing that kept them alive through the years," Crosley said. "I think it was especially hard on dad, probably because he was away with the National Guard when Billy disappeared."
"For a long while after Billy disappeared he was different. He was deeply hurt. I think what hurt the most was that he wasn't there," Martin said. "Mother told me that at one point he was so depressed that he contemplated suicide. I'd have understood it if he had, it was so much to bear."
Billy Martin's disappearance made national headlines as members of local and state authorities, the FBI and the National Guard combed areas around Clay County looking for the boy.
"People from all over said they read about Billy," Martin said. "This story reached as far as Colorado, that we know about."
Throughout the years there have been many stories and theories circulating around Billy Martin's disappearance.
"Oh, we have heard them all," Martin said. "This is such a gigantic mystery for such a small town, that everyone has a story."
To this day Martin and Crosley say they are still approached by people who want to share their ideas about what happened, and while most are well intentioned, some have been less than helpful.
"Our holidays were always in limbo because people would call to say they had seen him alive somewhere or knew where his body was. I knew a lot of them had good intentions, but it hurt so much," Martin said. "After a while, I just stopped answering the phone during the holidays. It was better to tell my parents it was a wrong number instead of telling them the truth."
Crosley agreed, but said her school days were especially hard because of one story that circulated in the community. According to the story, after being killed, the murderer disposed of Billy's body in the foundation of Meridian Elementary school, which was under construction at the time of his disappearance.
"There were days when I would be walking through the hallways of the school wondering if my little brother was underneath my feet," she said. "We didn't know a lot of the stories circulating around Billy's disappearance until we got older. I don't believe most of them, but I have thought about contacting a psychic. But when I think about it I have to ask myself, 'do I really want to bring it all back?'"
After Billy disappeared it changed everyone's lives in the neighborhood and around Brazil, according to Martin.
"Parents watched their kids closer than ever before," he said. "Every mother knew where every kid was and if they didn't know, they called each other to find them. You didn't get too far from a watchful eye."
Martin and Crosley have taught their children to be ever-watchful parents, admittedly, sometimes to the point of being overprotective.
"Back then we didn't know about sex offenders, or that people would do these types of things," Crosley said.
"We didn't have the technology back then that is used today, but it really doesn't matter. It only takes a minute for a child to disappear."
Both Martin and Crosley urge parents to get their children identified through a law enforcement agency.
"Please protect your child in any way you can," Martin said. "Our brother's disappearance is a huge mystery that it appears we will never have an answer to. If Billy hasn't been found by now, he probably never will be found. We don't want another family to go through the tragedy we have."
"It looks like we might have to wait until we die, like our parents," Crosley said with tears in her eyes, "to find out what happened to our brother."