From Wikipedia:
Einsatzgruppen (German for "mission groups", loosely translated as "task force") were paramilitary groups operated by the SS before and during World War II. Their principal task, in the words of SS General Erich von dem Bach-Zelewski at the Nuremberg Trial, "was the annihilation of the Jews, gypsies, and political commissars."
According to their own records, the Einsatzgruppen operatives are responsible for killing over 1 million people, almost exclusively civilians, without judicial review and later without semblance of legality (no reading of sentences of martial or administrative law), starting with the Polish intelligentsia and quickly progressing by 1941 to target primarily the Jews of Eastern Europe. The historian Raul Hilberg however estimates that between 1941 and 1945 the Einsatzgruppen murdered over 1.4 million Jews in open air shootings.
I'm pretty sure that Einsatzgruppen "Keller" was the name of a unit, rather than the owner of the watch.