"In Florida, the gun that prosecutors say Nikolas Cruz used at that Florida High School was an A-R 15-that police say he bought legally, despite having shown some threatening behaviors in the past.
And in New York State, even with one of the nation's toughest gun control laws, chances are, he could have also bought it legally here."
Nope.
You can't buy a regular AR-15 type rifle in New York state anymore.
By "regular" I mean one that has the form factor that is commonly associated with AR-15 type design.
There was supposedly some kind of re-design that was supposed to be New York State "compliant", but whether that ever got to market, I can't say (I live in Connecticut, where you can't buy a traditional AR-15, either).
Even if you own an older AR-15 style rifle that you acquired before the "SAFE Act" was passed, I don't believe you can sell it or even give it away as part of your estate after death. The rifle must be surrendered for destruction. At least to be compliant with the law.