Detectives are scouring footage from 300 CCTV cameras covering a six square mile area in the search for missing Alice Gross.
Police investigating the disappearance of the 14-year-old say the security film is "crucial" to their investigation, as they try to piece together her last known movements.
Police are continuing to search scrubland next to the Grand Union Canal Some 30 investigators are painstakingly reviewing the material, as dozens more officers continue to carefully search scrubland next to the Grand Union Canal in west London where the schoolgirl was last caught on CCTV.
A Metropolitan Police spokesman said: "This continues to be a massive investigation.
"A range of officers and staff from across the Met are taking part in the ever-expanding search for Alice.
"To date the search has involved the Met's underwater and confined space search team, marine support unit, search dogs, air support unit, Territorial Support Group, local borough officers, volunteer police cadets, visual images identification and detections officers, plus licensed search officers."
Alice has not been seen since August 28 Alice was last seen on CCTV walking along the towpath next to the canal as it passes under Trumpers Way at 4.26pm on August 28 but has not been seen since.
A reconstruction staged by police in the hope of jogging people's memory led to 150 calls from the public.
Alice's family have said "every morning brings new agony" as they made a heartfelt plea for her to return home.
More than a dozen police forces have contributed specialist resources to help with the search.
A range of officers are taking part in the ever-expanding search Detective Superintendent Carl Mehta said: "CCTV is clearly crucial in our investigation, but we still need the public's help and I want to hear from anyone who saw Alice during the afternoon of the Thursday she was last seen.
"In over 30 years of policing I have never seen such a strong community reaction. This is a community that is totally behind the search to find Alice and bring her home."
Investigators said an area of disturbed earth at Elthorne Park in west London, which runs beside the canal towpath, was no longer of interest.
A police reconstruction led to 150 calls from the public Prime suspect, 41-year-old builder Arnis Zalkalns - a convicted murderer who served seven years in a Latvian jail for killing his wife - was spotted on CCTV cycling along the same path as Alice on the day she vanished.
He has not been seen since September 3 and has not accessed his bank account or used his mobile phone.
But Det Supt Mehta stressed the Latvian, who was also accused of molesting a 14-year-old girl in 2009, was just "one line of inquiry".
A reward of up to £20,000 is being offered for anyone who has information that leads detectives to find Alice.

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