Its not conjecture.So conjecture then. Got it.
The USA knows who did it, but they play a strange game when it comes to formally acknowledging it so they play with the words.
Remember when the US said NK was behind the sony hack? That was the first time they openly, and controversially, attributed the attack to someone.
If NK relations weren't so bad, the US wouldn't have done it. Its to people who can challenge us, that we don't openly attribute attacks.
its political calculus.