Manchester attack: Bomber was planning attack for months, report says

Manchester Suicide Bomber Salman Abedi: A Timeline of Terror

Investigators are piecing together recent events in Salman Abedi’s life that led to the Manchester Arena suicide bombing attack that killed 22 people. Here’s what we know so far

The Manchester Arena bomber in last month's deadly attack at an Ariana Grande concert had been planning the incident for months, a report said.

Salman Abedi, his brother and father had been under surveillance since he arrived in Libya, officials in the country told the BBC. Abedi, who detonated a bomb at the arena on May 22, killing 22 people, had been planning to carry out the attack since December, according to security officials. Abedi died in the blast.

MANCHESTER ATTACK: SUSPECT VISITED SYRIA AND HAD 'PROVEN' TIES TO ISIS, FRENCH MINISTER SAYS

Greater Manchester police have been piecing the 22-year-old's movements in weeks following the bombing. Officials released photos of him in Manchester walking through the streets and rolling a blue suitcase, which may have contained bomb-making materials. They also released photos of a white Nissan Micra seized in Manchester, saying "significant evidence" had been found inside.

Twenty-two people were arrested in connection with last month's attack, however they have been released without charge, British police announced on Sunday. Authorities made the arrest on suspicion of terrorism offenses during their search for the "network" of people that helped the bomber leading up to the day.

MANCHESTER TERROR ATTACK SUSPECTS: WHAT WE KNOW SO FAR

Police believe Abedi built the carefully assembled bomb himself, though it's still unclear "whether he acted alone in obtaining the materials for the device ... and whether others knew or were complicit in the storage of materials knowing what was being planned," Russ Jackson, head of counterterrrorism policing for northwest England, told The Associated Press.

Detailed photos of the bomb revealed that it was packed with shrapnel — created to cause as much damage as possible.

MANCHESTER BOMBING SIGNALS NEW ISIS STRATEGY OF TARGETING CHILDREN

Abedi, who was born in the United Kingdom to Libyan parents, traveled Libya four days before the attack, police said. He apparently fooled his parents by telling them he was heading to a pilgrimage in the Muslim holy city of Meccas, reports said. He is believed to have traveled to Syria weeks before and showed he had "proven" linked to the Islamic State group.

Just before detonating the bomb, Abedi called his mother and said, "Forgive me," Special Deterrent Force spokesman Ahmed bin Salem said. Abedi's mother and three siblings in Libya were summoned for questioning earlier in the investigation. Abedi's brother Hashim and his father are still being held for questioning in Libya. Hashim is accused of knowing about his brother's plans.

The Associated Press contributed to this report.