New York is so proud of their “Red Flag” gun law, they use pictures of apparent teenagers to brag about it:
https://www.ny.gov/programs/red-flag-gun-protection-law
That leaves me with three possible explanations. Not listed in order of likelihood, nor are they mutually exclusive:
1. The New York authorities were negligent an an important life or death issue;
2. New York authorities knew about the shooter and wanted him to do what he did;
3. The law is worthless.
The political hierarchy simply needs to ignore the current laws in order to usher in the next level of restrictions.