Yep, you read that right. While Shmoop may not be the world's foremost punctuation experts (although we stand by our oxford commas with the conviction of… convicted people), we couldn't resist taking a stab at talking about those all too conspicuous em dashes in the poem. What in the world are they doing there? Quite a bit, it turns out.
Line 9: The first em dash of the poem comes at a moment of hesitation for our speaker. Sandwiched between those two becauses, the em dash tells us that he's not quite sure what he's trying to say here. Or if he is sure what he wants to say, he's not quite sure he believes it. Either way, it's clear that his reason for killing the other man—that he was a foe—is not quite cutting the mustard in terms of clearing his conscience.
Line 14: Things are getting really disjointed here. The speaker is starting to describe the life story he has imagined for the man he killed, but he interrupts his own story to remind his audience that he's just like the dead man. That interruption really hammers home the point. After all, if you're willing to interrupt your own story, that means you've really got something to say.
Line 15: Two more em dashes appear as the speaker tries to imagine a life story for the man he killed. What's with all the stuttering? We think it's telling us that the speaker's spitballing, so to speak. He's imagining things as he speaks, which lends both a sense of realism to the poem, and reminds us that this dude is seriously flailing. He's searching for a reason that he killed this man and coming up empty every time.