What We Know

• A bomb exploded outside Manchester Arena on Monday as an Ariana Grande concert was ending, killing at least 22 people and wounding 59 others.
• The bomber, who was killed in the explosion, was identified as Salman Abedi, 22, of Manchester.
• ISIS claimed responsibility for the bombing, but officials have not verified that claim.
• Security Management created a master list of references and resources for security professionals on stadium and soft target security. Access them, for free, here.
• The United Kingdom raised its terror threat level from severe to critical, meaning that a further attack may be imminent.

Ariana Grande Puts "Dangerous Woman" Tour on Hold

Update: 3:10 p.m., May 24, 2017

Ariana Grande is putting her "Dangerous Woman" tour on hold following the Manchester Arena bombing, the pop star said in a statement.

"Due to the tragic events in Manchester the 'Dangerous Woman' tour with Ariana Grande has been suspended until we can further assess the situation and pay our proper respects to those lost," the singer's management team said in astatement obtained by CNN.

The postponement means Grande's performances scheduled for tomorrow and Friday in London will be canceled, along with a show in Switzerland on June 5.

"We ask at this time that we all continue to support the city of Manchester and all those families affected by this cowardice and senseless act of violence," the statement continued. "Our way of life has once again been threatened but we will overcome this together."

Bomber's Brother, Father Arrested Abroad

Update: 3:00 p.m., May 24, 2017

Authorities have arrested two family members of the Manchester Arena bomber, Salman Abedi, as they continue to investigate whether he was working with a network to carry out the attack.

Libya counterterrorism officials arrested Abedi's younger brother, Hashem Abedi, who The Washington Post reports was suspected of planning an attak in Tripoli.

The Post spoke to Ahmed Dagdoug, a spokesman for Libya's counterterrorism Reda Force, who said Hashem was in "frequent contact with his brother Salman in Manchester and was aware of the plans to attack the concert."

Authorities also arrested Abedi's father, Ramadan, on Wednesday. Ramadan, known as Abu Ismail, spoke to The New York Times earlier this week and said that he did not believe his son carried out the attack at the arena.

"His ideas and his ideology were not like that," Abu Ismail said. "He was born and raised in Britain. He's a British citizen and he does not hold such ideologies."

What Security Professionals Can Learn from the Manchester Attack

Update: 12:35 p.m., May 24, 2017

Following the Manchester Arena bombing, Security Management reached out to several crisis management and soft target security experts to find out what security professionals can learn from the attack.

One of those experts was Michael J. Fagel, a crisis management expert with more than 30 years of experience in emergency planning and response. He sat down with Associate Editor Holly Gilbert Stowell to talk about the attack and what security professionals can do to prevent future similar attacks.

Stowell: From what we've seen over the last few months, attacks on soft targets--places of worship, study, and leisure--seem increasingly commonplace. What type of target is the Manchester Arena--a typical soft target, or some sort of hybrid with unique features?

Fagel: It is a typical soft target, given the fact that there are more and more security measures in place as people get closer to the venue. It's a pretty common occurrence in stadiums, to have nonsecure areas where people are approaching the building. Just think of an airport, think of a baggage claim, think of queuing up before you get in the airport. Everybody's milling about in these commons spaces before they go through security.

Continue reading their conversation by clicking here.

Manchester Attack Victims Named

Update: 11:00 a.m., May 24, 2017

Twenty-two people were killed in the Manchester Arena bombing, and the Greater Manchester Police Department said it is "confident" it knows the identity of all of the individuals.

Twelve victims have been named by their families, The Guardian reports:

• Jane Tweddle-Taylor, 51
• Nell Jones, 14
• Martyn Hett, 29
• Angelika Klis, 40
• Marcin Klis, 42
• Georgina Callander, 18
• Saffie Rose Roussos, 8
• John Atkinson, 28
• Kelly Brewster, 32
• Olivia Campbell, 15
• Alison Howe, 45
• Lisa Lees, 47

The National Casualty Burea has an emergency number available for those concerned about anyone who may have been impacted by the Manchester Arena bombing. The number to call is: 0800 096 0095.

Details Begin to Emerge about Arena Bomber

Update: 10:45 a.m., May 24, 2017

Two days after the Manchester Arena bombing, new details have emerged about Salman Abedi, the man who carried out the attack on Monday night.

Abedi was born in Manchester and was the son of Libyan immigrants, who moved back to Libya after spending decades in the United Kingdom, The New York Times reports.

Abedi had visited Syria and also went to visit his parents in Libya, who raised concerns to him about his radicalization, according to an individual who spoke with The Times.

He was known to security services, The Guardian reports, but Abedi was "not part of any active investigation or regarded as a high risk." Instead, he was "viewed as a peripheral figure in much the same way as the Westminster attacker, Khalid Masood."

Authorities are still working to determine where the bomb Abedi used was created, and if he had help assembling the device.

"It seems likely--possible--that he wasn't doing this on his own," said Britain's Home Secretary Amber Rudd.

SM is Signing Off for the Night

Update: 5:15 p.m., May 23, 2017

Security Management is signing off for the night and will not be providing updates to this post until tomorrow morning at approximately 10 a.m. EST.

For live updates, follow feeds from The Guardian and theBBC.

UK Raises Terror Level from Severe to Critical

Update: 5 p.m., May 23, 2017

The United Kingdom is increasing its terror threat level from severe to critical.

"It is a possibility that we cannot ignore that there is a wider group of individuals linked to this attack," said UK Prime Minister Theresa May.

The Joint Terrorism Analysis Center has been monitoring intelligence throughout the day, and based on its findings May said it is raising the threat level.

"This means not only that an attack remains highly likely but that a further attack may be imminent," May said.

With the raising of the threat level, Operation Temperer is now in force,The Guardian reports,and armed police who normally protect the Houses of Parliament and other sites in the United Kingdom will be replaced with military personnel.

DHS official: No Plan to Make Security Changes Due to Manchester Arena Bombing

Update: 3:20 p.m., May 23, 2017

A U.S. Department of Homeland Security (DHS) official who spoke to ABC News said there are currently no plans in place to make"significant security changes" in the United States in response to the Manchester Arena bombing.

"The DHS official said that the federal security posture in the U.S. is already at high levels and that there is not much more to be done in the aftermath of the attack," ABC News reports.

DHS issued a statement hours after the attack on Monday, saying it was closely monitoring the situation and is working with its foreign counterparts to obtain additional information about the incident.

"At this time, we have no information to indicate a specific credible threat involving music venues in the United States," DHS said. "However, the public may experience increased security in and around public places and events as officials take additional precautions."

Manchester Arena to Remain Closed

Update: 2:10 p.m., May 23, 2017

Manchester Arena announced that it will postpone two concerts scheduled for later this week due to the bombing on Monday.

In a statement via Twitter, the arena said it will postpone two shows by Take That, an English pop group, on Thursday and Friday.

"We are assisting the police in any way we can," Manchester Arena said on Twitter. "We cannot praise the emergency services enough for their response and have been inspired by the way the people of this great city of Manchester rallied round last night and have continued to respond today. It shows the very best of this city."

Take That was scheduled to perform in Liverpool tonight, but announced that it would bepostponing the showas a sign of respect to those affected by the Manchester Arena bombing.

Ariana Grande has not cancelled any future dates for her Dangerous Woman Tour, but Entertainment Weekly reported that her team is assessing whether to continue.

"Right now, the focus is on the victims and grieving for them. We're not focused on the tour," a source told EW.

Grande's next performances are scheduled for London's O2 arena on Thursday and Friday. The venue released a statement earlier today saying that it is working with Grande's promoters and will provide an update on whether the concerts will go on as planned.

Authorities Identify Manchester Arena Suspected Bomber

Update: 1:30 p.m., May 23, 2017

UK authorities identified the suspected bomber who carried out the attack on Manchester Arena as Salman Abedi, 22, who was born in Manchester, the BBC reports.

"Abedi, who had at least three siblings, and lived at several addresses in Manchester, including a property at Elsmore Road, Fallowfield, which was earlier raided by police," according to the BBC.

Police are still working to confirm if Abedi planned the bombing alone, or was working with others to carry out the attack. Greater Manchester Police Chief Constable Ian Hopkins declined to provide further details about Abedi toThe New York Times, and also said that a coroner has not officially identified him.

"The priority remains to establish whether he was acting alone or as part of a network," Hopkins said.

Experts Say Bombing Points to Vulnerabilities

Update: 12:15 p.m., May 23, 2017

Stadiums and event spaces often have metal detectors, bomb detection technology, cameras, and security guards inside. But the attack at Manchester Arena shows the need for more vigilance in areas outside security zones, an expert told The Los Angeles Times.

Michael Downing, executive vice president of security for Prevent Advisors, told the Times that extra attention needs to be paid to transportation centers, walkways, and parking lots at event spaces.

"Obviously, we are going to have to look at ingress and egress," he said, because terrorists tend to target areas where large crowds gather.

Other security experts who spoke with Reuters said they expect countries around the world to tighten security ahead of major cultural and sporting events following the bombing. However, they do not anticipate that these measures will stop determined attackers.

"Whatever is done--and in this case it's British intelligence which is considered among the best in the world--it won't prevent such incidents happening," said Jean-Charles Brisard, president of the Centre for the Analysis of Terrorism.

"You can bring back the perimeter, add security gates, and as many controls as you want, but that will not change the fact that a determined individual will carry out his act if he is not caught before."

Bombing at Manchester Arena Kills at Least 22 People, Injures Scores More

Update: 11:15 a.m., May 23, 2017

A man detonated a bomb at Manchester Arena Monday night, killing at least 22 people and injuring scores more in the deadliest terror attack in Britain since 2005.

The bomber, who has not been identified, was killed in the blast, and ISIS has claimed responsibility for the bombing; however, the terrorist organization's claim has not been verified.

ISIS claimed the attack as revenge against "Crusaders,"according to Reuters. "But Western experts were skeptical, noting it had offered two accounts of the attack partly contradicting each other and the British police version."

The 21,000-seat Manchester Arena was full of teenagers and their families on Monday night for a concert by American pop star Ariana Grande.

As the concert was ending, around 10:30 p.m. local time, a blast tore through the entrance hall next to the Victoria Station and concertgoers panicked to exit.

"There was this massive bang. And then everyone just went really quiet. And that's when the screaming started," Ryan Molloy, a concert goer, told the AP. "As we came outside to Victoria Station, there were just people all over the floor covered in blood."

Authorities closed the station and shut down public transportation from the arena, so many Manchester residents offered to allow concertgoers stay in their homes overnight.

Authorities are actively working to determine if the bomber acted alone, and if not, to identify and arrest his accomplices.

"The police said that they were canvassing leads and poring over surveillance footage to determine if the assailant, who died in the assault, had acted with any accomplices," The New York Times reports. "Shortly before noon on Tuesday, the police announced that they had arrested a 23-year-old man southwest of the city center 'with regards to last night's incident,' but they did not provide additional details."

Manchester Mayor Andy Burnham has also made plans to host a vigil on Tuesday night in Albert Square. "Whilst the area around Manchester Arena is still cordoned off, we want to remind people that Manchester will not be defeated, the city is open for business," Greater Manchester Police said.

This is an ongoing story. Security Management will continue to update this post as more information is confirmed and becomes available.