The younger artist is Walter Sickert, posthumously pegged as a Jack the Ripper suspect. Maybe you already noticed but you didn't put a TL note or whatever. It checks out, him being German born and Whistler's apprentice:

https://en.wikipedia.org/wiki/Walter_Sickert

I think Cuvie did a fakeout of him being a serial killer but not Saucy Jack since Jack didn't take women captive as far as we know, he likely just killed them in the street except the last victim where they were alone for hours in a room together.

Sickert is a sympathetic side character in Alan Moore's From Hell which is about Jack. Check it out.