I think the gun analogy does not really work here: you cannot be held accountable for creating any part of a gun, in case of a murder.

You’re not making the gun, the programmers that wrote the DDoS program did. You’re firing it.

It’s more like, you and a bunch of your friends murder by getting together and flinging the victim with rubber bands until the victim actually dies. Just because all you did was fling a small percentage of the rubber bands and that wouldn’t have killed the victim on your own doesn’t change the fact that you participated in and committed a murder. Legal systems do not have loopholes that allow you to commit crimes like this. They only have loopholes for the ultra wealthy.