Nephthys
The Gr8est!!!!!!!!
Well the way the guy was found in the story he appeared in was that the detective noticed that he'd done a practice kill on a kidnapper he found on TV. Ah, and btw the killer only kills other murderers, mostly in prison, which is a clear pattern at least. From there he called the killer out on TV to kill him, which he did, only to reveal that the guy he killed wasn't him and they had only aired in the Kanto region of Japan (with the idea to continue through the rest of the world), which he chose because of that first practice kill. From there he narrowed it down to people connected to the police based on the killers actions, and a student based on the time of day he killed. Then he had all the police officers in Kanto's family's tailed until the killer kind of messed up.
But he lost to the killer in the end though, lol.
However, this relies heavily on familiarity with technology, which neither Holmes or Poirot are familiar with, so I don't see them replicating it.