For Australian Daryl Floyd, 43 years was never going to be enough to stop him looking for his older brother.
The 52-year-old was only 10 when big brother Terry never returned home for dinner one afternoon in 1975.
It was later presumed the 12-year-old had been abducted and murdered when returning from a friend's house.
Mr Floyd has now spent the last eight years digging for Terry's remains in an abandoned mine shaft near the Victorian town of Avoca, about a two hour drive northwest of Melbourne, 60 Minutes reported.
He is confident his brother is somewhere in the mine, a place he began searching when new evidence of the crime, which cannot be revealed, emerged in 2010.
It's this lack of closure which now drives Mr Floyd to continue hunting for his brother's remains.
"My brother does not deserve to be laying in that disgusting mine," Mr Floyd says.
"If the situation was reversed I think my brother would do it for me. He would persevere."
It's also about fulfilling a promise he made to his parents, he said.
"I'm going to honour that promise."
Mr Floyd has not been searching alone - he's the first to admit it wouldn't have been possible without the generosity of others.
And if he doesn't find Terry in this mine, he doesn't plan on giving up.
"You don't die not knowing," he says.