If you are involved in a shooting, part of the investigatiton will be to determine if you had a specific reason to kill
that individual. If you claim you don't know the person, never saw him before, etc. - if the police have the smallest suspicion that you're lying, they'll seize most of your mail, your computer, your filed letters, look at any shipping boxes in your home to see if anything links you to that person.
Anything you post on an on-line forum is "public record" if they can read it without logging in. If your computer has stored your ID/password so you don't have to log in to a "private" forum, they can read your comments too.
When people offer advice to others like
drag the body inside the doorstep, besides advocating tampering with evidence, a good prosecutor can probably find other examples of a "criminal mindset" to paint you as an unsavory type.
And just because you said "I'd shoot 'em all and let God sort them out!
" don't expect the DA to interpret that as a tongue-in-cheek statement. He'll point to the smiley face as meaning you'd laugh at the death of others.