A Muslim community worker has told BBC News that members of the public called the police anti-terrorism hotline warning about Abedi's extreme and violent views several years ago.
The Islamic State of Iraq and the Levant terror group claimed responsibility for the barbaric attack, which involved a home-made device packed with nuts and bolts which exploded in the venue's foyer as thousands of young people were leaving.
Hashem Abedi, Salman's younger brother, has been arrested in Tripoli by counter-terrorism police on suspicion of of Islamic State links.
Salman Abedi's father has spoken for the first time since his son's death and said: "We don't believe in killing innocents. This is not us."
Speaking from Tripoli, he told AP that his son is innocent and confirmed that British police have arrested another of his sons. This is believed to be a 23-year-old arrested in south Manchester yesterday.