The theories that have been proposed fall into several general categories.

The simplest — and the one that San Antonio police apparently favored from the beginning — is that Nicholas ran away.

He had a juvenile court date.

He was a troubled kid who had been in trouble before.

Running away from an impending court appearance is not implausible.

The fact that he was never found, never surfaced with a new identity in another city, and has never been in contact with his family in the decades since makes this theory increasingly difficult to sustain, but it has never been definitively disproved.

The second category involves foul play, either by strangers or by people Nicholas knew.