Manchester's police chief said Wednesday that it is "very clear" that suicide bomber Salman Abedi acted as part of a network when he carried out Monday's attack that killed 22 people and injured 59 at a pop concert in Manchester.
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Six arrests were made in connection to the attack. The father and brother of the attacker were arrested in Tripoli on Wednesday, Lybian security spokespeople reported. The attacker was known to the security services, British Interior Minister Amber Rudd said on Wednesday.
Part of that threat assessment is the fear that Abedi could have been working as part of a group of accomplices with possible links to militant groups who have the competence to plot and execute suicide bombings.
"The question is: Was he acting alone or was he part of a network of others who want to kill. That is what the investigation is focusing on," a source with knowledge of the probe told Reuters, on condition of anonymity.
"The concern is that there may be others out there who helped him to make the bomb. Making a bomb of this sort requires a certain level of expertise and competence," the source said.
Salman Abedi, 22, was born in Manchester to parents of Libyan origin.
"It seems likely, possible, that he wasn't doing this on his own so the intelligence services and the police are pursuing their leads in order to make sure they get all the information ... that they need to keep us safe," Rudd told BBC radio.
Asked if he was known to the intelligence services, she said: "the security services will know a lot of people, it doesn't mean they are expected to arrest everybody that they know but it is somebody that they had known before and I'm sure when this investigation concludes we'll be able to find out more."
British investigators told French authorities that the suspect in the Manchester bombing had probably travelled to Syria, French Interior Minister Gerard Collomb said on Wednesday.
"Today we only know what British investigators have told us - someone of British nationality, of Libyan origin, who suddenly after a trip to Libya, then probably to Syria, becomes radicalized and decides to carry out this attack," Collomb told BFMTV.
Pressed on how he knew Abedi had been in Syria, Collomb said this was the information that French and British intelligence services had.
Reuters was unable to independently verify the links to Islamic State or Syria.