An online holiday missive from ISIS depicting Santa Claus overlooking Times Square with an opened box of dynamite is believed to have prompted a wannabe martyr to bomb the subway on Monday.

“We meet at Christmas in New York… soon,” the message reads.

The obvious intent of the posting was what police believe is exactly what happened when 27-year-old Akayed Ullah came upon it.

“He sees this ISIS propaganda,” a senior law enforcement official told The Daily Beast. “ISIS was putting on this holiday thing inviting lone wolves… ‘Attack New York at Christmas.’”

For his particular mode of attack, Ullah seems to have decided upon a recipe offered by an article titled “How to Build a Bomb in the Kitchen of Your Mom” that was posted in the first issue of the Al Qaeda in the Arabian Peninsula’s online magazine Inspire seven years ago, a few months before Ullah came to New York from Bangladesh.

The article offers a choice of explosive devices. The Boston Marathon bombers chose the one involving a pressure cooker and fireworks. Ullah allegedly went for the simpler pipe bomb, which involved match heads, a Christmas tree light, and a 9-volt battery.

Shortly after 7 a.m. Monday, Ullah arrived by the A train in the Times Square station with the bomb under his coat, affixed to his chest with Velcro and plastic ties. He made his way to an underground pedestrian passageway. Surveillance camera footage shows him waiting until a good number of innocents were around him.

In the video, a man walking up the passageway momentarily conceals Ullah from full view. But then Ullah reappears on the tape just in time for him to be recorded putting his hands together. Police believe he had a wire in each hand and this is when he completed the circuit from the battery to the Christmas tree light, which in turn ignited the compacted match heads.

“Making the wires touch,” the official said. “Then the thing goes up.”

The device detonated with only a fraction of its potential power. A woman who was close enough to Ullah to be deafened by the sound almost certainly owes her life to him having been less than meticulous in his bomb building,

“A lot of little mistakes,” the official said. “Not one big one, but enough little ones that it didn’t work the way he wanted it to.”

Only three of the innocents in the passageway were injured, but no doubt all of them were terrorized. A number of them ran past 28-year-old Port Authority Police Officer Anthony Manfredini, who was patrolling the area. Manfredini had served five years with the Marines and had been in a bomb unit.

In moments, three of Manfredini’s comrades were also racing toward the danger that panicked commuters were fleeing. Port Authority Police Officer Sean Gallagher, 26, is also a former Marine. Port Authority Police Officer Drew Preston, 36, did three combat deployments while in the Army and has a wife at home who is eight months pregnant with their second child. Port Authority Police Officer Jack Collins, 45, is an attorney and certainly could have been doing any number of far safer things.

“New York City could not have had four better people on the scene at that time,” a fellow cop later said. “New York City couldn’t have had four better people on the scene at that time.”

Back on 9/11, Port Authority police officers had raced into danger at the World Trade Center. Thirty-seven of them had perished, the biggest loss ever suffered by a police department on a single day in American history.

But the four cops on Monday morning did not hesitate for so much as a heartbeat as they dashed on into the passageway

“They’re running in blind,” the fellow cop said. “It’s smoke-filled and debris filled, and they don’t know what they’re going into.”

Through the smoke, they made out a sprawled figure with burns and what looked like shrapnel wounds. The cops could see wires sticking out of his pants and his jacket. They could also see that he had a cellphone in his hand. That raised the alarming possibility he was about to detonate a secondary device.

The cops dove on Ullah to prevent him from doing anything. They had the phone out of his grip and both his hands cuffed when they were joined by two Port Authority sergeants and the first of many members of the NYPD.

“I did it for ISIS,” Ullah was heard to say.

Gallagher officially became the arresting officer. Ullah was placed on a stretcher and carried from the subway. The Port Authority cops came along as an ambulance took Ullah to Bellevue Hospital.

On another day at Bellevue, Jack Collins had seen the opposite of terrorism sparkle in the eyes of a 2-year-old who had been abandoned along with his 10-month-old sister at the Port Authority Bus Terminal.

“I’m looking at him, he’s looking right back at me,” Collins later said of that moment with the boy in 2011. “He was so good. You could see it.”

Collins saw intelligence and potential and tenderness.

“It’s all there in his eyes,” Collins would recall.

The 10-month-old began to fuss after Collins and his partner took the two be examined. Collins watched the boy touch his forehead to the baby girl’s.

“She looks up and smiles seeing him, he smiles seeing her,” Collins would recall.

The girl was still smiling when she fell asleep. Her brother kept protective watch. And what Collins would clearly remember was the sparkle in the boy’s eyes.

These six years later, Collins was back at Bellevue with an accused subway bomber whose eyes a senior law enforcement official described with a single word.

“Clear,” the official said.

But here was the clarity that comes with being absent of the qualities that had filled the boy. Ullah was so bereft of potential and tenderness that he had apparently sought meaning in murdering as many innocents as possible as he took his own life. He was now given his Miranda warnings.

“I did it for ISIS,” Ullah then repeatedly said.

Here was the clarity of purpose but absence of essential humanity, as was also evidenced by the 29-year-old void of a man who drove a Home Depot rental truck down the West Side Highway on Halloween, killing eight.

After this latest attack, police headed out to the two-story house on East 48th Street in the Flatlands section of Brooklyn where Ullah had settled with his family in early 2011.

As the police waited for a warrant, they used Brooklyn’s Best Hardware and Locksmith across the street as an impromptu headquarters. The owner, Alan Butrico, remembered when Ullah had first moved in. Butrico remained puzzled why the family had renovated the house though they apparently did not own it.

Butrico recalled that Ullah had worked for a time as a livery cab driver. A record check shows that Ullah had obtained the necessary class E license in 2011. It expired in 2016.

On occasion, Ullah parked his car so it blocked Butrico’s driveway. Butrico recalled that Ullah would take something of an attitude when asked to move the car.

“He got kind of cocky, like he was doing me a favor by moving the car,” Butrico told The Daily Beast. “He was like, ‘I’ll get there shortly.’”

Butrico noted that Ullah often did not respond when people in the neighborhood offered a greeting.

“He would ignore them,” Butrico said.

Ullah largely kept to himself.

“He used to sit in the park and meditate for hours,” Butrico said.

Butrico added, “A weird type of person.”

Butrico had noticed a change of late.

“A couple of months ago, I saw he started growing a beard,” Butrico said.

But Butrico was not alarmed. He never detected manifest malevolence in Ullah’s eyes.

“Just normal,” Butrico said. “He didn’t look like he wanted to kill somebody.”

Butrico offered, “I thought he was shy.”

In more recent days, Ullah had worked for an electrical contractor whom people think is his brother but police say is in fact his cousin. They have been renovating a coffee shop at 39th Street and Eighth Avenue.

At some point, Ullah apparently came upon the ISIS holiday missive online.

And on Monday, Butrico found himself watching a copy of a search warrant arrive via his fax machine and pass into the waiting hands of the police. They were now building a case against Ullah.

The mass of cops had deterred a number of students from attending that day’s instruction at the Acting Out drama school on the corner. Those who were determined not to allow some bomber to change the course of their lives included 10-year-old Quinn Breslin. He was the kid on Santa’s knee in the Saturday Night Live cold open on Saturday. He was not about to miss his voice class on Monday.

“The show goes on,” his father, Kevin Breslin, noted.

Quinn’s eyes are definitely of the sparkly variety, filled with the opposite of terrorism, with what actual heroes such as those four Port Authority cops are defending in this seemingly endless war against clear-eyed crazies.

On Monday, the actions of the Port Authority cops roused White House press secretary Sarah Sanders to say something even the most passionate Trump hater could not rightly dispute.

“Port Authority Police Department Officer Jack Collins apprehended the terrorist, along with several other officers,” Sanders said. “These brave first responders and the others who rushed to the scene are heroes. On behalf of the president and a grateful nation, we would like to thank them and commend them for their bravery.”

Here was one thing on which all of America could agree.

On Monday night, the ISIS holiday missive was still out there on the internet. And there will be other missives and no doubt others to answer the call to murder. But there will also be brave souls such as serve with all the law enforcement agencies in New York and every other city.

Back before his death at the World Trade Center on 9/11, Port Authority Police Officer Antonio Rodrigues advised his fellow officers not to count on any big wins in the fight against evil, but also never to stop trying.

"The struggle is the only victory," Rodrigues would say.