On Sunday, New York City learned during police commissioner Ray Kelly's 60 Minutes interview that his police department had the capacity to shoot down an aircraft. This turned out to be a somewhat far-fetched claim, involving a 50-caliber sniper rifle mounted in a helicopter that couldn't have prevented the 9/11 attacks. But on Wednesday, Journalist Murray Weiss pointed out in his column on DNAinfo that the Secret Service keeps a much more serious anti-aircraft battery on the island: Shoulder-launched, heat-seeking Stinger missiles that most certainly could take down a hijacked jetliner. Weiss says he learned about the weapons cache while researching a book on 9/11.

In a book I wrote called The Man Who Warned America, I reported that after the Towers fell, several law enforcement agencies that kept clandestine offices there showed up to help in the rescue efforts, but also searched for their secret stashes of documents and weapons.

“The Drug Enforcement Administration wanted to find the records of cases they had built against drug dealers, while CIA operatives came to the crumbled towers to get into secure safes that had held stacks of classified information and documents in a phony office they had set up," I wrote.

"The most closely guarded secret in the towers was kept by The Secret Service, which was concerned about a Stinger missile, which was used to protect the president in the event of an attack when he visited New York.”

Of course, shooting down a jetliner over Manhattan wouldn't exactly avoid catastrophe, so it's just as well the Stingers are to be used only to protect the president, who generally keeps his visits brief.