] 22 people killed in the deadliest attack on the UK in over a decade. Authorities are now racing to find out how and why.>> I'm Reuters Jacob reporting from Downing Street. But for those here, a suicide bomber on British soil poses two key questions. The degree of help the culprit had, and how the explosives went undetected.
>> A man has been arrested in connection with the attack. Analysts say the nature and success of the bombing indicates it was well thought out.>> Clearly, there has been some planning involved here. An individual managed to get into the concert hall and his device was able to go off.
It's still a relatively low order. It's a nail bomb. Nail bombs are pretty unsophisticated, but they do have the consequences in terms of mass. Horrific casualties, which is what sadly happened here.>> Police point to an improvised explosive device as the weapon of choice, one that makes it hard for security services to detect.
>> While all the high-end technical plots have been thwarted to a greater extent, it was the low-level ones that are very difficult to ultimately police. Whether it's taking a car, or randomly driving it into innocent civilians, or in this case, a very simple to make nail bomb.>> In March, the UK faced a lone self-radicalized attacker armed with a vehicle and knife.
Two months on, the UK prime minister again forced to respond to an attack.>> We now know that a single terrorist detonated his improvised explosive device near one of the exits of the venue, deliberately choosing the time and place to cause maximum carnage and to kill and injure indiscriminately.
>> The bombing in Manchester comes with the UK in the midst of a general election. After the chaos of Monday night, campaigning has now been suspended. But counter-terrorism operations are in full swing.