Last Updated May 25, 2017 5:42 PM EDT
MANCHESTER, England -- A spokesman for the anti-terror force in Libya says the 22-year-old bomber in thetelephoned his mother hours before the attack and said, "Forgive me."
Special Deterrent Force spokesman Ahmed bin Salem said Thursday that's mother and three of his siblings in Libya were summoned for questioning.
Bin Salem says the mother told interrogators that her son left Libya for England only four days before Monday night's bombing and called her on the same day of the attack. He says Abedi "was giving farewell."
The young Briton is accused of killing at least 22 people and injuring 59 others by detonating a suicide bomb during an Ariana Grande concert at Manchester Arena. Abedi died in the attack.
Authorities say he may have been more directly connected to the Islamic State of Iraq and Syria (ISIS) than they had originally believed. The terror group claimed responsibility for the attack.
Another sibling, 18-year-old brother Hashim, and Abedi's father were arrested in Tripoli on Wednesday. Eight men are now in custody in connection with the attack.
Bin Salem and Libyan investigators believe "the bomber acted alone," based on what Hashim told them -- that Salman learned how to make explosives on the internet and he wanted to "seek victory for the Islamic State."
Since the deadly attack, police have carried out a number of raids around the southern Moss Side district of the city, where Abedi lived with his parents and two siblings.
Authorities have found more evidence -- including leaked photos of the remnants of the bomb itself -- that suggest the attack was the work of a terror network. The images show a shredded backpack that the device was allegedly carried in, metal bolts, and screws that were used as lethal shrapnel.
British authorities have expressed outrage over the leaked photos, which were shared with American counterterrorism officials. Police say the leaks compromise their investigation due to the fact that the public is now aware of what authorities are looking to track down.
British Prime Minister Theresa May raised her concerns over alleged intelligence leaks from the bombing investigation with President Trump. A British official confirms that May discussed the matter with Mr. Trump after they posed with other NATO leaders at a summit in Brussels on Thursday.
The U.S. and British leaders talked again later, sitting next to each other at a working dinner. May looked stern, while Trump waved his hands. May stressed "that intelligence that is shared between law enforcement agencies must remain secure."
Manchester police stopped providing information to the U.S. about the concert bombing after photos of the crime scene appeared in the New York Times, though it was not clear where the images came from. Athe U.K. is now sharing intelligence with the U.S.
May says the nation's terrorism threat level will remain at critical, meaning another attack could be imminent.