The next time someone says we need to start pounding on the doors of our immigrant communities to “find out what the hell is going on,” remind them of Adnan Fazeli.

Fazeli, 38, died on a battlefield in Lebanon last year after leaving his home and family in Freeport to become a fighter for the Islamic State in Syria.

As reported in Tuesday’s Portland Press Herald, he came to the United States in 2008, became radicalized after moving to Portland from Philadelphia in 2009 and, as time passed, became increasingly isolated from his family and the local immigrant community before suddenly hopping on a plane for the Middle East in August of 2013.

And how do we know all of this now?

Because those closest to him called the FBI, that’s how.

A federal government affidavit, obtained by Press Herald staff writer Scott Dolan, identifies them only as “CI 1,” “CI 2,” “CI 3” and “CI 4.” (“CI” is shorthand for “Cooperating Individual.”)

But a close reading of the document leaves little doubt that some if not all of them were closely connected to Fazeli during the roughly four years he spent with his wife and children first in Portland, then in Westbrook and finally in Freeport.

As Ebrahim Fazeli, Adnan Fazeli’s nephew, told staff writer Megan Doyle, “Our family were the ones that initiated this investigation. We did it long before all these terrorist organizations were in the news.”

It’s a murky world, to be sure. Maine State Police Detective George Loder, acting as a member of an FBI task force, noted in the affidavit that the FBI paid three of the four informants for their information on Adnan Fazeli.

But this much is clear: Without that information, it’s highly doubtful Fazeli would have been so much as a blip on the FBI’s radar screen a full 17 months before he was killed in a battle with the Lebanese army on Jan. 23, 2015.

Noted Loder in the affidavit, “On August 23, 2013, CI 1 told a local FBI agent that CI 1 believed an individual named ‘Abu Nawaf’ (an alias used by Adnan Fazeli) had converted from a Shia to a Sunni Muslim. CI 1 reported further that Nawaf was an Iranian national then residing in Freeport, Maine, and had recently grown a beard and had become very religious …

“CI 1 had overheard Nawaf expressing anti-American rhetoric while at an Iraqi market in Portland, Maine, where Nawaf was known to associate.”

The tips kept coming: “CI 2” told the FBI that Fazeli “at some point changed and became very angry.”

“CI 3” provided Fazeli’s back story from Iran to the United States, where he “did not adapt well” and eventually became radicalized.

“CI 4” provided details of that radicalization, from Fazeli’s conversion to Wahhabism, a puritanical form of Sunni Islam, to his penchant for watching Islamic videos on YouTube.

The good news for Maine is that Fazeli took his anger elsewhere. Ten days before the FBI’s first interview with “CI 1,” Fazeli boarded a Lufthansa flight from Boston to Frankfurt, continued on to Istanbul and never returned.

But what if he had stayed in Maine?

What if, rather than join the fight over there, he’d resolved instead to start one of his own right here in the belly of what he perceived to be the American beast?

Suddenly those “cooperating individuals” would no longer just be helpful sources in solving a puzzle that self-destructed halfway around the world – and thankfully, according to the FBI, left no co-conspirators back in Maine picking up where he left off.

No, with Fazeli still in our midst, our very lives might depend on those informants’ willingness to step forward and sound the alarm.

So with that in mind, what’s the buzz in the wake of Tuesday’s stunning headline?

With painful predictability, both Gov. Paul LePage and U.S. Rep. Bruce Poliquin reflexively went after President Obama, claiming that Fazeli is the latest example of an immigration system that LePage called an “utter failure.”

What neither acknowledged is that no system, short of an outright ban on all immigration, can account for the individual who goes off the deep end only after arriving here and deciding for whatever reason – too much time alone on the internet? – that America is the enemy after all.

Nor does a tighter border (or higher wall) protect us from the terrorist who is actually born here and enjoys all the rights and privileges of a U.S. citizen before he turns on his own country. (See: Orlando nightclub shooter Omar Mateen.)

Our only protection against those threats is advance warning. And our only hope for such warning begins and ends with the eyes and ears of those who realize, before anyone else, that something’s not quite right with an Omar Mateen or … an Adnan Fazeli.

More than once in recent months, Republican presidential nominee Donald Trump has called for monitoring mosques throughout this country and, if necessary, shutting some down altogether.

Speaking in Ohio just this week, Trump called for a Commission on Radical Islam that would develop “new protocols” for law enforcement officials as they go about investigating possible terrorist threats.

That may be red meat for the xenophobic masses. But if you’re a new arrival to this country, wondering nervously whether you should drop a dime on a suspicious countryman and thus invite law enforcement into your life, it translates into four easily understood words: Keep your mouth shut.

Ebrahim Fazeli showed no such compunction when, upon learning that his unhinged uncle had gone off to fight with ISIS, he picked up the phone and called federal authorities.

Nor did Adnan Fazeli’s brother, Portland physician Jabbar Fazeli, who told the Bangor Daily News that he too alerted authorities about his brother. He finally decided to go public, Dr. Fazeli said, as a “lesson” to future immigrants with information worth sharing.

That takes courage.

It takes integrity.

And now more than ever, it deserves our heartfelt thanks.