Police remain unsure whether killer Salman Abedi acted alone or with accomplices

Detectives investigating the Manchester Arena bombing still remain unsure whether killer Salman Abedi acted alone or with accomplices in a terror network.

The 22-year-old detonated a device at the end of an Ariana Grande concert on 22 March, killing 22 people, including seven children, and injuring more than 100 others.

A total of 21 people have been arrested suspicion of terrorism offences but the final two who were being held were today released from police custody.

Nobody has been charged in relation to the attack and police are searching a landfill site for a suitcase they believe Abedi may have used to store explosive materials used to make the bomb.

Police have today released new images of Abedi waking through Manchester with the blue suitcase, which could contain crucial evidence.

Last week, Abedi's brother Hashem, 20, told Libyan investigators working alongside British police in Tripoli that he had helped his brother buy components for the bomb in the UK, but claimed not to know the details of his plan.

It is believed that the device was put together at various addresses used by Abedi in Manchester before he targeted the pop concert.

Police have released new images of Abedi walking through Manchester with a blue suitcase, which they believe contained bomb materials he discarded after assembling the device

Police have released CCTV images of Salman Abedi as he made his way around Manchester

Pictures show the terrorist hauling the blue suitcase through the streets before the attack

Police have searched 29 houses and found evidence of explosive materials at several locations, each with links to Abedi.

Russ Jackson, head of counterterrorism policing for northwest England, said police believe Abedi assembled the bomb himself.

But he said it was 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.'

Jackson said some of those arrested had offered 'accounts which explain innocent contact with Abedi.'

He said risk to the public had been considered before suspects were released.

Barrels like this were stored in the car, which Abedi used to store bomb making materials

Key to the investigation is this white Nissa Micra, in which Abedi stored bomb-making items

Greater Manchester Police issued photos of the Nissan and a red and black holdall and appealed for anyone who recognised either to come forward

Suspects arrested under terrorism laws can be held for up to 14 days before they must be charged or released.

He revealed that Abedi, who left the UK on 15 April and travelled to Libya before returning on May 18, had sought to transfer money out of the country before the attack.

Key to the investigation is a white Nissa Micra, in which Abedi stored bomb-making items.

Det Chief Supt Jackson said the bomber had been tracked buying nuts from a DIY store that were used for shrapnel as well as the tin which is thought to have contained the explosive.

Det Chief Supt Jackson said they wished to interview Abedi's younger brother, Hashim Abedi, 20, who also left the UK on 15 April.

He is been detained in Libya along with his father Ramadan, 51.

It has been reported that Hashim Abedi told the militia group holding him that he helped his brother buy the bomb-making equipment in Britain and he'd insisted the device was not smuggled into the country.