To be honest, in any given terrorist attack, knowing the location and victims often gives you a pretty good idea of who the perpetrators possibly are.
This goes for Muslims as well as white supremacists, and any other ideology, faction, or group.
But we need to be careful about instantly blaming certain groups of people, and the de facto group that individuals will lay the blame on for any given terrorist attack usually has more to do with that individual themselves and what other sociological groups they have in their mind as "other", those that they tribalistically turn into enemies.