John Doe/Jane Doe

[poli]

This means unknown person. In Colombia the letters initials nn are used to mean this. Is nn used elsewhere?

[AngelicaDeAlquezar]

According to the law, you can't publish the names of suspects or people involved in a legal process, so Mexican media use the name and N, or their initials.

· Los tres sospechosos, Jonathan N., Pedro N. y Eulalio N. fueron detenidos en un bar de Cuernavaca.
The three suspects, Jonathan N., Pedro N. and Eulalio N. were arrested in a bar in Cuernavaca.
· El presunto asaltante, JHL, escapó con rumbo desconocido.
The alleged robber, JHL, escaped to an unknown location.

Sometimes it gets a bit ridiculous, because we all know the names of the people because we've been following the news, but as soon as they get in the legal process, their full names can't be used anymore.
Such is the case of a man involved in the bribes done by Odebrecht to Pemex, so they'd do business in the oil industry; his name, Emilio Lozoya, was all over the press as the scandal was known, but since he's involved in a complicated legal process, he became Emilio N. or Emilio L.
And the funniest one I saw, a guy whose nickname was "el licenciado Carmona", who became "Miguel Ángel N.", as if the nickname didn't give away his full name.

When you don't actually know the person's name, the authorities say something like:
· La víctima del asesinato permanece en calidad de desconocida.
The victim of the murder hasn't been identified yet.