Actually, there were other assassins who tried to kill Hitler prior to Staufenberg, i think there was a total of 41 attempts but only a few got really close, like a watchmaker who hid a bomb in the munich Hofbräuhaus which didn’t went off or another person who shot at Hitler but due to him wearing a steel helmet didn’t kill him.
Personally, i think no assassination attempt at Hitler was wrong (and i am not only saying that because i am austrian and so required by law to have that opinion).Hitler was responsible for the deportation of 6.5 million jews, introduced church taxes to lower the popularity of christianity (after the war he would have most likely started a religious cult combining elements from some norse and persic religions mixed with a leader-cult), and would have had future plans for the spreading of his master-race by human-breeding-projects. And i guess he’s now somewhere in hell.
So considering all that, i think murdering Hitler wouldn’t have been a very… evil… sin even if committed by a civilian.