Acc. to "Tagesschau" 4 people in custody, 2 from ATC (the ATCO and her superior) and the "leading engineer for snow plowing", one from the "Flugaufsicht" (what ever that is in RUS). Director and deputy director of the airport have resigned according to the same article....
In German:
Nach Unfall auf Moskauer Flughafen: Festnahmen nach Tod des Total-Chefs | tagesschau.de
The snow plow driver has amended his statement - his lawyer said - "he might have had a few drops of alcohol".
I guess Mr.Putin is on a crusade....