Looking for the grave of Markus Mordechai SPERLING who was shot near Lubaczow in 1942

Markus Mordechai SPERLING was the son of Josef Leib SPERLING  and Sheindel Sala SPERLING nee STRASSBERG..

He was  born between in 1892 in Wielcy Oczy near Lubaczow according to the indexes on Jewish Records Indexing - Poland .Siblings found in the same indexes:Eidel born 1879,
Chajm Hirsch born 1881, Moses Isak born 1883, Gerschon born 1885 and Chane Mindel born 1886. According to this Markus Mordechai SPERLING was the youngest among his siblings.

He lived in Rynek 9 in Lubaczow with his wife Luba (Lieba?) nee WEISS and their two daughters and their son Jakob SPERLING, born ca 1930.

According to his two surviving daughters,  Markus Mordechai SPERLING was shot to death in the forest outside Lubaczow in  1942 (תש"ב).
His son Jakob SPERLING and Markus Mordechai's wife Luba SPERLING, born 1904,  were also murdered in Holocaust.

According to their knowledge, a Jewish man managed to bury Markus Mordechai Sperling at the Jewish cemetery in Lubaczow and also put a stone on his grave. 

Considering that this was during the second German occupation and that I have found no gravestones from this period, my theory is that he put a stone on the grave, but that the stone had no inscription.