A police officer stands by a cordon at the scene where a body was found during the search for missing schoolgirl Alice Gross in west London yesterday.

London Evening Standard/London

Police searching for missing schoolgirl Alice Gross launched a murder investigation yesterday after finding a body hidden in the River Brent.

Detectives called the discovery “devastating” and said Alice’s family had been informed. They said “significant efforts” had been made to conceal the corpse, found less than half a mile from where she was last seen alive.

Talented musician Alice, 14, was last seen on August 28 walking on the Grand Union Canal towpath in west London. The body was discovered late Tuesday night near where her rucksack was found a week after she vanished and within a mile of her Hanwell home.

It is also near where convicted murderer and prime suspect Arnis Zalkalns, from Ealing, was filmed on CCTV riding his bike the day she disappeared.

Questions were being asked yesterday about why it took police so long to find a body, amid fears that crucial trace evidence may have been lost.

The case has been the biggest search operation since the 7/7 bombings but officers have been unable to trace 41-year-old Zalkalns since he disappeared a week after Alice. There are fears he has fled to his native Latvia.

Met Commander Graham McNulty, leading the investigation, said yesterday: “We are unable to make a formal identification at this stage but clearly this news is devastating for everyone involved in the search for Alice.

“My thoughts are with Alice’s family and friends. This is now a murder investigation and I need the public’s help to find whoever is responsible.

“Our work at this scene is crucial to ensure we capture all the available evidence allowing us to identify who is responsible for this dreadful crime.

“This may take some time and I ask people to remain patient with us. I can confirm that significant efforts were made to conceal the body.” He thanked the community for their help after people draped thousands of yellow ribbons across homes, shops and notice boards in the area. He urged anyone with information to come forward, saying it was “not too late”.

The body was recovered by search and rescue teams on a stretch of the River Brent next to Ealing Hospital.

A source close to the case told the Standard the body was found as an officer carried out a fingertip search of the riverbank. The source said: “He thought, ‘This isn’t right’. The earth appeared to have been disturbed and rather than wait till morning officers started there and then to search that position in the river.” The spot is “a number of metres deep”, said the source, adding that police had found an item on the body which “confirmed it was Alice”.

Police tape today stretched across the road leading to Green Lane, a neighbouring cul-de-sac of detached homes.

Dozens of officers were stationed on the towpath to protect the scene where forensic teams and specialist divers have been working for several days.