The National Center for Missing and Exploited Children estimates that on any given day, there are tens of thousands of open missing persons cases in the United States.

Most of these involve adults — individuals who have the legal right to leave without explanation — but thousands involve children whose disappearances remain unexplained.

The vast majority of missing children cases are eventually resolved: the child is found, or their remains are identified, or a credible explanation for their absence emerges.

A smaller number persist without resolution — cases where the initial investigation found no evidence, where the trail went cold, and where decades pass without answers.

Nicholas Barclay is in this smaller category.