Why did the elders of Israel sprinkle dust on their heads?
Joshua 7:6 (ESV)
6Then Joshua tore his clothes and fell to the earth on his face before the ark of the LORDuntil the evening, he and the elders of Israel. And they put dust on their heads.
The elders of Israel are included to show the national nature of the lament. They put dust on their heads as a sign of mourning (see Job 2:12; Lamentations 2:10).
6 Then Joshua tore his clothes and fell to the earth on his face before the ark of the LORD until the evening, he and the elders of Israel. And they put dust on their heads.