This site for Grünthal, Ottomar from 2/KG-66:
http://www.aircrewremembrancesociety...anPilotsG.html
Has this description:
KIA 31 August, 1943; crashed during a sound-proofing (?) mission, 8.5 km east of Villaroche, by Petit Plessig, cause unknown. Remaining crew (KIA): Lt Karl Reitzenstein, geb 6/5/1919, Obs; Uffz Josef Ries, geb 2/11/1918, R/O and Gefr Karl Marschall, geb 1/20/1922, 1/Wart. Source: B.Bines.