I often wondered who would be bothered most with the first kill. I thought maybe Donnie, since he's smart enough to see the whole picture.
Then, Mike came to mind; he's so sensitive and caring - not that the others arent', but, fun-loving Mikey would have some issues with taking a life. And, I was right. :0) Don's the perfect brother to comfort him, too. :0) Of course, he's my favorite.
As for Leo, well, I never really expected him, but I'm not terribly surprised, either. I think Splinter (from FanFiction) wrote a one-shot dealing with the first-kill aftermath. It's Leo-centric, but I'm not sure of its title.
Anyway, there was one instance where you used a comma just before the word, 'and'. Whenever you use 'and', it replaces a comma, unless there are three or more trains of thought in the same sentence. Here is the sentence in question - There was a long pause, and regret weighed heavy in the air.
Then, right after that in the next sentence, you didn't put a comma after the word 'Finally'. Whenever there's a subtle pause - such as with that word, a comma helps to augment that pause. For example - Finally, Donatello whispered to Mike "I don't know, Mike. I just don't know..."
Anyway, this was a great little one-shot and I loved it at the end, where you dropped down to the first bunk to show Leo wrestling with the same issues as Mike, yet knowing far more than his siblings about the purpose for which Splinter trained them.
Nice job all around! :0)
Be blessed,
Rene'