The people who destroyed the WTC on 9/11 died in the act. There was no trial that would convict them posthumously of terrorism, given that we do not judge the dead (well, not anymore: it used to be a thing, see [1]). So, their criminal records are clear of terrorism convictions.

Does that mean that I will be labeled as a spreader of fake news if I call Mohamed Atta [2] a terrorist?

[1] https://en.wikipedia.org/wiki/Cadaver_Synod

[2] https://en.wikipedia.org/wiki/Mohamed_Atta