The most dramatic part, of course, is the first one; it's a powerful
image, and kudos to you for thinking of it. But that is also the main
thing wrong with your poem; you give the best first, and after that
it's all downhill. I'd suggest you do some shuffling, moving LL1-4 to
the bottom and starting the poem with L5; and also cut "Beheading" in
what's now the last line, let the reader think you're talking about
"leaving town" or the like on the train. If it were me I'd play with
that ambiguity more, talk about the train as a "fast way to go" and
such. But at minimum move those 4 lines; that's essential.