Cold cases are occasionally cracked after years of frosting over, but even more go unsolved, and the longer they remain open, the more notorious they become.
Murders, disappearances and other crimes the authorities can't crack often strike a chord with conspiracy theorists, armchair investigators and amateur internet sleuths who think they're smarter than the law, and the debate they spark among these circles usually burns hot.
Modern history is awash with unsolved crimes, sometimes because the perpetrators planned it meticulously and covered their tracks, at other times because the investigators made critical errors, and occasionally it's a little of both.
Such cases, however, stretch back across the ages to a time when records had only just begun. Every once in a while, modern advancements in fields such as forensic science yield breakthroughs in these enduring criminal mysteries, but cases that remain unresolved for more than a decade usually stay that way.
Even after that length of time and longer, the internet never seems to give up trying to put these mysteries to bed...