UK police arrest fifth person in connection with Manchester attack (credit: REUTERS)

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A cousin of the terrorist who carried out a suicide attack against innocents at a pop-concert in Manchester, England last week was discovered to have posted antisemitic messages to social media, The Jewish Chronicle citing the Times of London reported Monday.Abderahman Forjani, 21, made disparaging remarks about the Jewish community in a series of online posts, with one stating: “If only Hitler was still alive –these Jews would be burnt in chambers.”Forjani had also posted anti-UK messages, including derogatory comments about his hometown, writing: "Manchester is my no.1 enemy I f***ing hate the s***hole.”Forjani and his older brother Abdalla, 24, were arrested last Tuesday following the Manchester Arena attack the previous night.The barber shop that the two brothers ran, called Fade Away, was raided by police on Friday, according to The Jewish Chronicle.Meanwhile, Britain's MI5 domestic intelligence agency announced Monday that it will hold an inquiry into how it dealt with public warnings that the Manchester suicide bomber Salman Abedi posed a potential threat, the BBC reported on Monday.MI5 was alerted to Abedi's extremist views at least three times, the BBC said.It is highly unusual for British authorities to make public that the security service is conducting an internal investigation into possible lapses.Interior Minister Amber Rudd told Sky News that this was a "right first step" for MI5 to take in the wake of the bombing that killed 22 people at a pop concert by US singer Ariana Grande.The security service will examine assumptions that were made about Abedi before the attack, and has launched a "post-incident investigation" into how the bomber was overlooked, the BBC said.