This is the NY statute on making a terroristic threat. It has to be a specified offense with reasonable expectation of imminent commission of the offense. None of the reporting so far suggests that 11 months ago, he was guilty of making a terroristic threat such that he should have been arrested at that time, and would have been convicted and sitting in prison 11 months later.
S 490.20 Making a terroristic threat.
1. A person is guilty of making a terroristic threat when with intent
to intimidate or coerce a civilian population, influence the policy of a
unit of government by intimidation or coercion, or affect the conduct of
a unit of government by murder, assassination or kidnapping, he or she
threatens to commit or cause to be committed a specified offense and
thereby causes a reasonable expectation or fear of the imminent
commission of such offense.
2. It shall be no defense to a prosecution pursuant to this section
that the defendant did not have the intent or capability of committing
the specified offense or that the threat was not made to a person who
was a subject thereof.
Making a terroristic threat is a class D felony.
I hope he rots in prison. But the solution to gun violence and hate crimes isn't more mass incarceration. And there's nothing to suggest that even had he been arrested 11 months earlier, anything would have been different yesterday. This is a sideshow from the utter lack of reasonable gun control measures and the huge rise in hate crimes in this country, which have been spurred on by the GQP and Fox News, among others.
Edit to add: There's also no reason to believe that the Buffalo PD, which threw an elderly man down during a Black Lives Matter protest, would have had any interest in actually trying to prevent white nationalist terrorism anyway.