Video report by ITV News security editor Rohit Kachroo
Police have released CCTV images of the Manchester suicide bomber on the night of the arena attack.
Police are trying to piece together Salman Abedi's movements from 18 May when he returned to the UK through to Monday night when he launched the deadly attack.
The 22-year-old last visited a city centre flat before making his way the Manchester Arena, police said.
On his back a rucksack is visible, which detectives believe could have held the explosive that tore through crowds exiting the Manchester Arena.
His features are partly obscured by a baseball cap and glasses.
"The flat is highly relevant as a location which we believe may be the final assembly place for the device," Greater Manchester Police Chief Constable Ian Hopkins said.
The CCTV images are the first to show what the 22-year-old looked like when he carried out the deadliest terror attack Britain has seen for more than a decade.
Greater Manchester Police did not reveal where it was taken or at what stage of the evening.
Police are searching 14 locations and 13 people have been arrested on suspicion of offences contrary to the Terrorism Act.
Mr Hopkins added: "In the past five days we have gathered significant information about Abedi, his associates, his finances, the places he had been, how the device was built and the wider conspiracy. As a result of the arrests and searches which have taken place we now have many further lines of enquiry. We already have more than 1,500 actions we are pursuing.
"This is still a live investigation which is not slowing down. Our priorities are to understand the run up to this terrible event and to understand if more people were involved in planning this attack."
The brother of suicide bomber Salman Abedi is among those detained.
ITV News understands Abedi called his younger brother just 20 minutes before the bomb was detonated.
The UK's terror threat level has been reduced from critical nearly a week on from the Manchester Arena which killed 22 people.
Anyone with information should call the Anti-Terrorist Hotline in confidence on 0800 789321.
If you have any images or footage that you believe can assist us then upload them to Ukpoliceimageappeal.co.uk or Ukpoliceimageappeal.com