THE hunt for the prime suspect in the disappearance of teenager Alice Gross looks set to escalate after search teams found a body in a river and launched a murder inquiry.

Convicted killer Arnis Zalkalns, who was spotted following the 14-year-old along a tow path when she was last seen, vanished nearly a month ago.

Scotland Yard has come under fire for delays in identifying the 41-year-old Latvian as a risk, and so far has not been able to apply for a European Arrest Warrant due to lack of evidence.

Yesterday ,(Wednesday) Metropolitan Police Commander Graham McNulty said that "significant efforts" were made to hide the body, which was found in the River Brent near Alice's family home in Hanwell, west London.

But he gave no further explanation as to why it has taken more than a month for any significant progress to be made in the hunt for Alice, despite the force holding the biggest search since the aftermath of the July 7 bombings.

Speaking at Scotland Yard, the senior officer said: "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.

"At this time my thoughts are with Alice's family and friends. I would ask you to respect their privacy and allow them space.

"This is now a murder investigation and I need the public's help to find whoever is responsible."

He added: "Even if you have not yet spoken out it is not too late to tell us what you know."

Alice was last seen on CCTV walking along a tow path beside the Grand Union Canal in west London on the afternoon of August 28.

Nearly three weeks later investigators realised that Zalkalns, who disappeared on September 3 and was reported missing two days later, had been cycling behind her.

He served seven years in prison in his native country for bludgeoning and stabbing his wife Rudite to death.

So far officers from Scotland Yard have refused to say where in the River Brent that the body was found. It runs a short distance from Hanwell and path where Alice was last seen.

Mr McNulty said: "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.

"At this point I do not wish to speculate any further on what has happened."

General labourer Zalkalns, who worked at a building site in Isleworth, west London, is thought to have come to the UK in 2007, but authorities here apparently had no record of his murder conviction.

Alice's disappearance prompted an outpouring of support in her local community, where yellow ribbons and bows still adorn the streets.

Posters are taped to walls, lampposts and car windscreens, while sunflower-colour strands of material are tied to doorknobs - many inscribed with a simple message: "Find Alice."

One barge owner, who has been living on the River Brent for two weeks, said he could not understand why the body had not been found sooner in the shallow water.

The man, who did not want to be named, said: "It is terribly sad if they have found Alice.

"But I can't understand why they didn't find the body the first time around. Divers have been here before, the river is only 3ft (0.9m) deep and there is no flow to it, so maybe they missed it first time around."

Leader of Ealing Council Julian Bell said that the yellow ribbons will be kept in place as a sign of respect.

"The news that a body has been discovered in the River Brent is devastating," he said. "Although no formal identification has yet been made our heartfelt sympathy and thoughts are with Alice's parents and sister during this difficult time.

"Today is the day that everyone in our community has dreaded and the yellow ribbons flying across our borough show how deeply our community cares and has been affected. It is essential that anyone with information that can help the police's investigation comes forward.

"On behalf of the community I would like to thank the police officers involved in the search for their dedication and perseverance.

"As a sign of respect, no ribbons will be removed until it has been discussed with Alice's family."