Police say Manchester attacker built bomb 'alone at his flat' Abedi most likely built the bomb used in the attack while "alone in his flat."

 -- Suspected Manchester Arena attacker Salman Abedi most likely built the bomb used in the attack while "alone in his flat," but investigators are still unsure of whether or not he had help carrying out the attack, police said Sunday.

Police said they now have an understanding of Abedi’s movements “almost hour by hour” in the days before May 22, when he allegedly detonated a knapsack bomb at the end of an Ariana Grande concert, killing himself and 22 others, according to police.

“We now have a deep understanding of Salman Abedi’s movements in and out of the country in the weeks leading up to the attack,” Russ Jackson, head of counterterrorism policing for northwest England, said in a statement Sunday.

"We understand how the chemicals and equipment were obtained and where the bomb was assembled,” Jackson added.

Twenty-two people who were previously arrested in connection with the terrorist attack have now been released and some of them were determined to have only had "innocent contact" with Abedi.

However, police are still looking to determine if other people may have helped him to obtain materials for the bomb or if others "were complicit in the storage of materials knowing what was being planned."

Police are also looking to speak with Abedi's younger brother Hashem, who has been detained in Libya, according to the Sunday statement.

Detectives believe Abedi, a 22-year-old Briton of Libyan descent, used his vehicle to store bomb parts. He was captured on CCTV putting plastic barrels into the vehicle.

Abedi purchased the vehicle, a white Nissan Micra, on April 13, just two days before he departed for a trip to Libya.

He returned to the UK on May 18, seemingly with "intent on committing the attack within days," police said Sunday, adding that the began to purchase more items for the bomb soon after his return.

The Greater Manchester Police department said the investigation has turned into one of the biggest that it's ever conducted, consisting of hundreds of witness interviews and more than 29 house searches.

"We have found evidence of explosive material at several locations. Each location has links to Abedi," Jackson said. "This is very much a live criminal investigation moving at considerable speed."