They might want to review their firearm policies for residents.

... then he wasn't "Responsible." That's textbook.

specifically for patients with Alzheimers and dementia allow any firearms to be kept by residents?

...many venue owners or operators do or do not permit/restrict firearms and other weapons. They made or failed to make an adequate assessment of threats and safety critical issues.

This is in New York State, right? If he has a New York State pistol permit (which he must have in order to legally possess any handgun), then he had to recertify his permit before Jan. 31, 2018. If he didn't recertify, his guns should have been automatically confiscated. If he did recertify, his recertification would have included his place of residence. If people who are under residential care for Alzheimer's and dementia are not having their permits revoked, then one can only conclude that the entire permit recertification requirement -- passed in 2013 as part of the "NY SAFE" Act -- is nothing more than a security-theater sham.

Add to this the fact that the facility itself failed to provide even minimal oversight to protect the safety of its residents, and you'll find plenty of people to blame other than "gungeoneers."

This man should not have had a gun. That's very clear.