Anyone who has taken an 8-year-old to a sold-out concert knows the protective feeling that comes over you at the end as you join the crush of people heading for the exits.

Your kid is giddy from the music and wishing it was not over, but also tired and wishing she could just instantly transport herself back home to text her friends and maybe post a few selfies and then hop into bed at the end of a night to remember.

You yourself are feeling all those things except maybe the texting and selfies part, and your bond with your kid is even closer for having just shared something magical.

What still separates you is that she is the child and you are the parent, and you snap alert in the crush to make sure you don’t lose track of her.

Her hand is small and vulnerable in your own. You hold it just firm enough not to lose her and pull her to you if it’s needed, but not so hard as to impart alarm.

The protective feeling intensifies with the bottleneck at the door but begins to ease as the squeeze lessens just beyond.

On the way in, you passed the security check here, a reminder of the continuing threat that has shadowed your daughter’s entire life. But the check also brought a reassurance that precautions were being taken against anything happening during the concert.

Now that the concert is over, there is no need for security at the door and you continue on out with no thought of a threat. That protective feeling further ebbs as you start across the broad public area toward the promise of home.

You would never expect that this would be the most dangerous moment and the most dangerous place.

At the Ariana Grande concert at the Manchester Arena on Monday night, this was the moment when a 22-year-old monster stepped from a silver car wearing a suicide vest and strode into an exiting crowd that included Lisa Roussos and her 8-year-old daughter, Saffie Rose.

The explosion was much too loud to have been mistaken for the popping of one of the pink balloons that had cascaded down from the ceiling after Grande did her encore and blew a kiss to the crowd. The cowardly atrocity was complete before even the most protective parent could have done anything at all.

Lisa’s sister, Ashlee Bromwich, was also there, and both were said to have been injured by the bits of metal that had been packed around the explosives to make the device deadlier. They are said to have been rushed to different hospitals, separated from each other as well as from little Saffie Rose.

When there was no immediate word of what happened to Saffie Rose, the mother of her best friend, Jessica Tinsley, went on Facebook.

“I’ve tried to contact Saffie’s mum and none of the messages have gone through on the phone,” Kate Tinsley wrote. “Jessica has gone to school today not knowing a thing. My daughter is best friends with her in school. Everybody is worried, the whole village. Everybody is in bits waiting for news, just some news that she’s okay, she’s alive.”

Other people went on Twitter. One tweet read:

“MISSING: Saffie Rose Roussos ,8yrs old

White Ariana t-shirt-denim skirt-black leggings-black boots.”

Then the Manchester police announced that Saffie Rose was among the 22 dead. A tweet on the Ariana Grande Today account read:

“ An 8-year-old separated by her mother and sister last night. May she rest in peace.”

The attack seemed to have been carried out by one man, but investigators doubted that this was another lone wolf.

“I can say that with a high degree of confidence that it was not,” a counterterrorism agent told The Daily Beast. “There was a high degree of sophistication to this.”

The explosive device in Manchester was deadlier than even the more accomplished lone wolves, such as the Chelsea bomber in New York, have been able to produce.

“A very well made device with a highly lethal charge,” a senior counterterrorism official told The Daily Beast on Tuesday.

And while the Chelsea bomber placed his device by a Dumpster that muffled the blast and killed nobody, the Manchester bomber detonated his suicide vest in precisely the place where he stood to kill the most people.

“The Chelsea bomber, that’s a guy who did a very good bomb, but didn’t do his homework,” the official said, then saying of the Manchester bomber, “This guy did an even better bomb and did his homework.”

Investigators figure there must have been surveillance before the attack, noting that the bomber chose a spot on the way from the arena exit to the trains, exactly where and when the crowd was thickest.

“A guy who had either done surveillance or it had been done for him to determine the best place and best time,” the official said.

Now, just as surveillance had told the bomber where and when to strike, those very factors told the investigators the nature of the attack.

“They learn by watching,” the official said. “We learn by learning.”

The investigators saw once again the potential value of the vapor wake detection dogs that are deployed in New York. The dogs can detect the airborne scent of explosives that are carried through an area even after the bomber has departed.

But it would have required considerable luck to detect and thwart the Manchester bomber in the few moments he took to proceed from his car to the area where he detonated the device.

And the bomber may not have been deterred had there been a heavy presence of uniformed cops and soldiers before the attack such as appeared in Manchester afterward.

Intelligence might have stopped him had there been any to tip off the authorities to this plan.

We should hope that similar carnage does not result from plots that might have been prevented had President Trump not—unwittingly or no—violated a promise by the U.S. not to pass on sensitive intelligence on ISIS that we received from Israel.

The plot that Trump mentioned reportedly had to do with explosive devices that can get past airport security.

The Manchester attack showed that a terrorist bomber can defeat any screening just by attacking people as they leave the protected area.

And the indications that this was not just a lone-wolf attack suggests that ISIS was introducing a whole new generation to terror by targeting a concert where a majority of the 21,000 who attended were in their teens or younger.

Eight-year-old Saffie Rose was not collateral damage.

She was a target.

She had been deliberately murdered with icy premeditation along with 21 others at the specific place and time that the bomber chose as the most likely to produce the highest body count. Twelve more children were among the 59 who were injured.

The youth of the victims and the concert setting had a deep effect on counterterror investigators, for many of them have kids of their own who attend such events. And many have gone along when the kids were younger and know the protective feeling that comes when you are exiting at the end.

“Our kids go to these things,” an anguished counterterror cop said Tuesday night.

The cop remembered aloud taking his daughter to a Miley Cyrus concert back in the pre-“Wrecking Ball” days. He recalled the voices around him as they exited.

“People are excited, they’re talking about the music and what they heard,” he said. “It’s almost like they can’t wait to get home to tell their friends and text their friends.”

He figures it must have been the same in Manchester just before the bomb went off and 22 people were silenced forever and the voices of the survivors turned to screams.

“And for what?” the investigator asked. “For what purpose?”

The investigator is a father who began the fight against terrorism at the World Trade Center on 9/11 and has been at it for more than 15 years with hardly a day off, seven of those years before Saffie Rose was even born.

“I don’t know,” he said. “I really don’t know.”