Salman Abedi called his mother and brother 15 minutes before he began his deadly mission to kill innocent people at the Ariana Grande concert in Manchester.
On the call, he told his mother: "Forgive me."
"He was giving farewell," a spokesman for the Libyan anti-terror Special Deterrent Force told AP.
He also spoke to his brother Hashem "15 minutes before the operation started", according to the spokesman.
Hashem has been arrested in Libya and he confessed to knowing "all the details" of the Manchester plot while under interrogation, The Independent reports.
The new details have emerged after authorities interrogated his mother and siblings over what they knew about his bombing attack on Manchester Arena on Monday night, which killed 22 people.
Eight men have now been arrested in the United Kingdom as police uncover an international terror network that was behind the atrocity. A woman detained on Wednesday was released without charge.
"I want to reassure people that the arrests that we have made are significant, and initial searches of premises have revealed items that we believe are very important to the investigation," Greater Manchester Police Chief Constable Ian Hopkins said on Thursday.
Authorities are also following up Salman's apparent links to terrorist operatives elsewhere in Europe, North Africa and the Middle East. He is believed to have travelled to Libya and Syria in the weeks leading up to the attack.
Salman's family is also in the frame for investigators. His older brother Ismail, 23, has been arrested in Manchester, and his father Ramadan and younger brother Rashem, 20, have been arrested in Tripoli.
His mother Samia and younger sister Jomana, 18, were also been brought in for questioning.
FATHER OF SUICIDE BOMBER'S CHILLING POST
The father of the Manchester bomber once posted a chilling message on his Facebook page in praise of a notorious terrorist and accused mass murderer.
New details about Ramadan Abedi have surfaced after his 22-year-old son's deadly attack.
Mr Abedi was arrested by a Libyan militia, the Special Deterrence Forces, on Wednesday over his alleged links to Islamic State.
But a post on his Facebook page from 2013, Mr Abedi shared a picture of Al-Qaeda operative Abu Anas al-Libi and described him as a "lion".
"The prophet knows how many people have (posted) the image of this lion on their (Facebook) profile ... The weak are forbidden from sharing," he wrote, in comments translated from Arabic.
Elsewhere on his page, Mr Abedi posted a picture of his son Hashem brandishing a machinegun. In the caption, Mr Abedi said his son was "practising".
n the Facebook profile, which has been inactive since October 2013, Mr Abedi goes by the name Yousef Hannaa. He also goes by the name Abu Ismail.
Like Mr Abedi and his wife Samia, Mr Al-Libi was a Libyan national who fled the Gaddafi regime in the 1990s and moved to Manchester.
Mr Al-Libi was later accused of playing a role in the 1998 bombings of US embassies in Kenya and Tanzania. The explosions killed 224 people, including 12 Americans and injured more than 4000.
After the attacks, Mr Al-Libi became one of America's most wanted, and a bounty of $5 million was put on his head.
He reportedly acted as the body double of September 11 mastermind Osama bin Laden because he was tall and bore a resemblance to him.
He was captured by US authorities in 2013 but died 17 months later, days before he was due to face trial on multiple charges, including terrorism and murder.
He denied playing a part in the bombings.
Mr Abedi worked as a security officer under Muammar Gaddafi's dictatorship in his native Libya but fled when he was accused of tipping off Islamists about police raids.
He and his family were granted political asylum in the UK, and lived in Manchester for at least a decade.
He, his wife and two youngest children Hashem and Jomana returned to the capital Tripoli after Gaddafi was overthrown, leaving his sons Salman and Ismail behind. Salman died in the Manchester Arena attack and Ismail has been detained by British police over his alleged involvement in the bombing.
Before his arrest on Wednesday, Mr Abedi professed his son's innocence.
"I don't believe it was him," he said, according to The New York Times.
"His ideas and his ideology were not like that."
WHY SALMAN MAY HAVE DONE IT
Salman Abedi's sister has given an insight into the life of an angry young man, which may explain why he carried out the deadly attack on Manchester Arena.
Speaking to The Wall Street Journal, Jomana Abedi, 18, said her brother was a kind man who wanted "revenge" for injustices inflicted against Muslims.
"I think he saw children - Muslim children - dying everywhere, and wanted revenge," she said.
"He saw the explosives America drops on children in Syria, and he wanted revenge.
"Whether he got that is between him and God."