The would-be subway bomber Najibullah Zazi, whose attempted attack on New York in September 2009 is described in detail in the new book “Enemies Within: Inside the NYPD’s Secret Spying Unit and bin Laden’s Final Plot Against America.”

The book alleges that just months after the twin towers fell, a new anti-terrorism program was born within the New York Police Department. The idea was to turn plain clothes cops into intelligence agents to track the city’s Muslim population.

But authors Matt Apuzzo and Adam Goldman argue that the controversial unit fell short when it mattered most: When Zazi, loaded with a detonator and explosives, drove a rental car across the George Washington Bridge and into Manhattan. …

The scope of the NYPD’s intrusive domestic surveillance programs, built with help from the CIA, was “staggering,” said Apuzzo. Such programs were designed to catch someone like Zazi – a homegrown, radicalized, al Qaeda-trained guy from Queens who wanted to blow up the subway. But they didn’t.