MANCHESTER, England - As investigators hunted for possible accomplices of a suicide bomber, thousands of people poured into the streets of Manchester in a vigil Tuesday for victims of a blast that bathed a pop concert in blood - the latest apparent battle-scarred target of Islamic extremists seeking to rattle daily life in the West.
PHOTOS: Terror attack at Ariana Grade concert in Manchester
The attack left at least 22 dead, including an 8-year-old girl, shattering the revelry at the close of a show by American singer Ariana Grande, where strains of electric pop and the sways of innocent young fans quickly gave way to an explosion, a flood of screams and a stampede of panicked concert-goers, many clutching pink balloons and wearing the kitten-ear headbands popularized by Grande.
Touching on that disconnect, British Prime Minister Theresa May said: "We struggle to comprehend the warped and twisted mind that sees a room packed with young children not as a scene to cherish but as an opportunity for carnage."
May said Britain's terror threat level had been raised to critical - meaning another attack may be imminent. The status means armed soldiers could be deployed instead of police at public events including sports matches. The threat level had been at the second-highest run of "severe" for several years.
The Islamic State group claimed responsibility for the horror, which also wounded 59 people, though a top American intelligence official said the assertion could not be verified. Manchester Police Chief Ian Hopkins identified the bomber as 22-year-old Salman Abedi, who authorities said died in the attack. Police raided two sites in the northern English city, setting off a controlled explosion in one, and arresting a 23-year-old man in a third location.
Britain raises terror level to 'critical' after Manchester attack
May said Abedi was born and raised in Britain. A European security official, who spoke on condition of anonymity because he was not authorized to comment on ongoing investigations, said Abedi was of Libyan descent. There was no information released on the man who was arrested.
At least 20 heavily armed, helmeted police surrounded a modest red brick house listed as Abedi's address in a mixed Manchester suburb at midday on Tuesday and blasted down the door.
"It was so quick. These cars just pulled up and all these police with guns, dogs, jumped out of the car and said to us: 'Get in the house now,'" said Simon Turner, 46, who lives nearby. Later, forensic officers in white coveralls were seen going in and out of the property.
Details on Abedi were slow to trickle out. He was described by neighbors as a tall, thin young man who often wore traditional Islamic dress, but few said they knew him well.
Alan Kinsey, 52, who lives across the street, said his neighbor would often get picked up by another young man in a Toyota and often returned late at night. "I thought he worked in a takeaway or something" because of his late hours, Kinsey said.
Police also searched an apartment in a nearby area that British media reported belonged to Abedi's brother, Ismail.
Late Tuesday, thousands of people, some holding up signs proclaiming "I Love MCR" - an abbreviation for Manchester - held a moment of silence at a vigil for the victims. Lord Mayor Eddy Newman and the city's police chief were among the speakers in front of City Hall in Albert Square. A banner with a website for a Muslim group said "Love for all, Hatred for None."
Monday's bombing made Manchester Arena, one of the largest indoor concert venues in Europe, the latest apparent target of Islamic extremists striking at the heart of Western culture, an ideology baffling to the panicked young faces emerging from the concert.
Among those confirmed killed was Georgina Callander, whose death was reported by her former school, which posted a photo of her in her school uniform on its website and described her as a "lovely" and "very popular" young woman. Also killed was 8-year-old Saffie Roussos, who a teacher called "simply a beautiful little girl in every aspect of the word" who was warm, kind, "and unassuming, with a creative flair."
Besides the dead, the wounded included at least 12 children under the age of 16, hospital officials said.
Grande, who was not injured in the blast, tweeted: "broken. from the bottom of my heart, i am so so sorry. i don't have words."
The bombing took place after Grande closed the show with "Dangerous Woman" and left the stage and the audience streamed toward the city's main train station. It scattered bolts and other metal scraps, apparently intended to maximize the bloodshed. People tumbled over guardrails and one another clawing toward an escape.
"There was this massive bang. And then everyone just went really quiet. And that's when the screaming started," said 25-year-old Ryan Molloy. "As we came outside to Victoria Station, there were just people all over the floor covered in blood."
The attack sparked a nightlong search for loved-ones - parents for the children they had accompanied or had been waiting to pick up, and friends for each other after groups were scattered by the blast. Twitter and Facebook lit up with heartbreaking appeals for the missing.
"I've called the hospitals. I've called all the places, the hotels where people said that children have been taken and I've called the police," Charlotte Campbell tearfully told ITV television's Good Morning Britain breakfast show. Campbell's 15-year-old daughter, Olivia, had attended the show with a friend who was wounded and being treated in a hospital.
"She's not turned up," Campbell said of her daughter. "We can't get through to her."
Hayley Lunt, who brought her 10-year-old daughter Abigail to the show, her very first concert, said they ran as fast as they could once the explosions rang out. "What should have been a superb evening," Lunt said, "is now just horrible."
Some concert-goers said security had been haphazard before the show, with some people being searched and others not. However, authorities would not say whether the bomber blew himself up inside or outside the arena, so it wasn't clear if rigorous bag screening or additional security would have helped prevent the deaths and injuries. The venue tweeted on Monday night that it happened "outside the venue in a public space."
Around the United Kingdom and across Europe, the attack brought fear and mourning.
At Buckingham Palace, Queen Elizabeth II marked a moment of silence along her husband Prince Philip as well as Prince Charles and his wife Camilla. In Rome, the lights of the Colosseum and Trevi Fountain were darkened.
U.S. President Donald Trump, on a visit to the West Bank city of Bethlehem, called the perpetrators "evil losers" and said "this wicked ideology must be obliterated."
Manchester, 160 miles (260 kilometers) northwest of London, is one of Britain's largest cities. The attack was the deadliest in Britain since four suicide bombers killed 52 London commuters on subway trains and a bus in 2005.
Islamic State's claim of responsibility echoed others the group has made for attacks in the West but with vague details that left open the possibility it was an opportunistic attempt at propaganda. Manchester itself has seen terror before, but not this deadly. The city was hit by a huge Irish Republican Army bomb in 1996 that leveled a swath of the city center. More than 200 people were injured, although no one was killed.
The bombing also elicited painful memories of the 2015 terror attacks in Paris, where most of the 130 killed were at the Bataclan concert hall.
CONCERT SECURITY BEEFED UP AFTER BOMBING
Concertgoers at Allstate Arena, where The Weeknd headlined Tuesday night, arrived to officers in tactical gear, long security lines and police on the roof keeping an eye on the crowd.
"I think it's necessary considering what happened yesterday, but I wish it wouldn't have to be like this," said Eliza Martin, concertgoer.
In Rosemont, fans were undeterred.
"I just think that when something scary happens you shouldn't let anything else kind of scare you from doing things that you want to do," said Zakiyah Toor, concertgoer.
Concert security under review after Manchester explosion
Ariana Grande's former bodyguard, Hector Garcia, who was also formerly the head of security at Soldier Field, said one of the most alarming aspects of the Manchester attack was that it took place at the end of the show.
Security experts say their focus at big stadium events is generally on people entering an events, and metal detectors at the entrance of such events are becoming standard. But none of that made any difference Monday night because the suicide bomber waited until the end of the show and never went through the metal detectors.
"Because of this incident, now we have to be more concerned not only with the ingress, we have to worry about the egress, and so that makes it that much tougher to deal with," Garcia said.
Garcia recently worked as a bodyguard for Grande, and while she was unharmed in the incident he said he knows she is deeply affected by the tragedy.
"She has to understand it wasn't her fault. It had nothing to do with her. This is just bad people who did bad things, and she just happened to be in that scenario," he said.
Garcia said the bombing should serve as a wakeup call to stadium operators around the country. In Rosemont, the police handle security for Allstate Arena. They have beefed up their presence Tuesday night, and the general manager of the arena, which hosts dozens of concerts a year, said, "...in light of yesterday's events, concert-goers will see an even greater police presence tonight. Concert-goers are reminded that no backpacks or liquids are allowed into the Allstate Arena, and that all persons entering the venue are subject to magnetic screenings and pat-downs."
Chicago security ready in wake of Manchester attack
Chicago has several large music and sports venues. What is being done to keep places like Wrigley Field and the United Center safe from a terror attack?
Experts said there is no perfect security, but there is better security. Venues across Chicago are working to improve, especially at places where thousands of people gather.
"You want to have a larger presence outside of these events to act as a deterrent," said Erin Grudzinski of Hillard Heintze Security.
Thousands of people will gather at Wrigley Field Tuesday evening, even as the dark cloud of the Manchester terror attack hovers over it.
"I've been a fan my whole life, he's been a fan all his life. He's never been here. I knew they would do the best to protect us. They will do the best they can do and we're here just to have a good time." Said Kim Crow, Cubs fan.
The attack on the Manchester Arena represents one of the first times suicide bombers have successfully inflicted a large number of casualties in the vicinity of a large-scale venue, highlighting the vulnerabilities of places like the United Center or Wrigley Field. Magnetometers secure the entrances, but the perimeters remain vulnerable especially as people gather to either enter or exit.
Terrorism experts said more metal detectors may have helped in Manchester, even though the apparent suicide bombing happened just outside the concert venue.
"The individual suicide bomber can use their own eyes to detonate the bomb when there is a large number of people around to kill," said Professor Robert Pape, terrorism expert, University of Chicago.
That's also the reason so much time and effort is also invested on security on the outsides of venues, and why the Cubs are giving the city $1 million to install 30 new cameras on city-owned light poles near Wrigley Field.
"This is about having a 360 degree view of the ballpark so that we can make sure that we have eyes all across the area, not just inside the area... because a lot of these incidents are happening outside the ballpark," said Julian Green, spokesperson for the Cubs.
With big summer concerts and large-scale events planned in the city, an attack like this can spark fear. But Chicago police said there is no immediate threat.
Terrorism experts also noted a frightening trend. In the past, foreign nationals would creep though the immigration system, planning attacks overseas. But that's not what the world is seeing now.
"They are issuing propaganda videos that they make overseas. Those are inspiring attacks, even when they may not have any direct connection," Pape said. "Just last week, ISIS released a 44-minute propaganda video with a British national calling for horrendous attacks against Britain. Now, a week later, this is what we see."
The Council of Islamic Organizations of Greater Chicago released a statement Tuesday strongly condemning the "callous and horrid" suicide bombing in Manchester. The group represents more than 60 Islamic institutions in the Chicago area.
"CIOGC expresses its collective prayers for strength and healing to the families of those victimized by this act of violence. Chicago Muslims also extend sincere sympathies to the community of Manchester at this time of loss. This was a heartless act of violence, directed at defenseless children. No social, political, or religious principle can justify the intentional killing of innocent children. We stand with all members of our global community that remain resilient in their resolve to maintain the rule of law and ensure the safety of their people," the statement said.
Cardinal Blase Cupich, Archbishop of Chicago, asked the faithful in a tweet Tuesday to pray for everyone affected by violence.
WLS-TV contributed to this report.