Some DC heroes have pasts that have made them into killers, whether it was because of being villainous at some point or because of mistakes they've made. There are some heroes out there who have caused deaths that make even the worst villains look like rank amateurs, whether it be because of mistakes or their own willful actions.
The Justice Society contains the most experienced heroes on Earth. Beating them all by a wide margin is the Spectre. The Spectre is God's Angel of Vengeance and has been doing the Lord's work since the beginning of time. Starting with battling fallen angels and moving into punishing mortals throughout the ages, the Spectre has been killing since not long after the beginning of time.
Even after bonding with slain cop Jim Corrigan, the Spectre kept up his murderous ways. He grotesquely tortured evildoers, ending their lives in ways that fit their monstrous crimes. The Spectre's kill count over the years is impossible to know. But when one has existed as long as he has, it's got to be a huge number.
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