An 18-year-old man has been arrested on suspicion of murdering Leonne Weeks, 16, who was found dead on a path in Rotherham.
Alice Gross Investigation
The Met Police have revealed they had enough evidence to charge a Latvian builder with the murder of west London teenager Alice Gross.
Detectives say the motive of convicted killer Arnis Zalkalns (pictured left) - who was found hanged four days after Alice's body was found in west London - was "most likely sexual".
Scotland Yard has revealed evidence which it says "points firmly" to the Latvian builder being responsible for the 14-year-old's abduction and death and the extraordinary lengths taken to hide her body in the River Brent.
Zalkalns' DNA was found on Alice's shoe and a cigarette butt at the crime scene, her iPhone case was discovered buried in his back garden and one of the bags used to conceal her body matched a roll of bags found at his workplace, the force said.
In a statement, Alice's family said there remained "serious unanswered questions" following her death after her suspected killer was allowed to move to the UK in 2007 despite being convicted of murdering his wife.
Zalkalns, 41, was found hanged in Boston Manor Park, west London, on 4 October 2014, four weeks after he was reported missing.
Speaking at Scotland Yard's headquarters, Detective Chief Inspector Andy Chalmers said the cause of Alice's death was asphyxia, caused by a larger body lying on top of her smaller body.
"We believe the most likely motive was sexual," he said.
"It was the same cause of death given for Tia Sharp."
Mr Chalmers said "great efforts had been made to carefully and deliberately hide the body".
Alice was found tied in a foetal position, wrapped in bin bags, which had been weighted down with a bike wheel and bricks and covered with six sections of a tree trunk in a pyramid formation, police revealed.
Fire crews were needed to remove the heavy tree trunks placed on top of Alice's body, which was naked apart from one sock. Most of her clothes have never been found.
"It was clear such efforts were taken to conceal the body, she was never expected to be found," Mr Chalmers said.
"Boy, do we wish we had found her earlier."
Alice was last seen alive walking along a towpath on August 28, while Zalkalns was caught on CCTV following her on his bike.
Despite the biggest police search since the aftermath of the July 7 bombings, it was more than a month before her body was found near her home in Hanwell, west London.
CCTV evidence suggested that Zalkalns would have passed Alice on the towpath at about 4.10pm, when he stopped for at least 80 minutes, police said.
Mr Chalmers said: "I strongly believe during this period Arnis Zalkalns killed Alice Gross."
When he reappeared on camera, Zalkalns's appearance indicated he might have been in the water and his trouser legs were rolled up, police said.
CCTV footage showed him buying beer in a nearby shop later that evening before he cycled on a different bike to the area where Alice was last seen. He returned on a further two occasions and had searched Alice's name online as reports of her disappearance emerged.
Zalkalns was last seen in a shop in South Acton in the early hours on September 4 when he bought food and water and carried a heavily-laden rucksack.
Tim Thompson, deputy chief Crown prosecutor for London, said: "There is no eyewitness evidence. The scientific evidence does not link Arnis Zalkalns directly to Alice death.
"Of all the people the various strands of evidence might have implicated, they in fact point towards Arnis Zalkalns: a person who has previously killed, and concealed, the body of a young woman."
Zalkalns, who had previously served seven years for murdering his wife Rudite in Latvia, is believed to have come to the UK in 2007, but authorities here are thought to have had no record of his murder conviction.
Police have also spoken to a woman, who initially refused to provide a statement following an alleged assault by Zalkalns in 2009 when she was 14. The woman has provided a statement on the incident which happened when she was "alone in open land near the canal" where Alice was found, Mr Chalmers said.
Scotland Yard has insisted it was "unlikely" that Alice's life would have been saved had the force known about Zalkalns' murder conviction before her death.
Detective Superintendent Carl Mehta said: "The evidence tends to suggest that Alice was dead prior to her parents ever realising that she was missing. I don't think that would have made any difference."
He added: "I cannot say with any certainty, if his conviction in Latvia was identified in 2009, that would have started steps to remove him from the country. However I think it is very unlikely."
Police said there is no evidence that Zalkalns was responsible for any other reported offences or that he had previously met Alice.
Mr Chalmers said Zalkalns' partner remained in the UK and was "clearly traumatised" by his actions.
In a statement, Alice's family said: "It remains impossible to describe the pain of losing Alice. Her death has left a hole in our lives that can never be filled.
"Every day is a reminder of her life and her loss, and it is hard to imagine a future in which we can find peace and healing.
"Her brutal murder remains shocking - an appalling senseless act that is still difficult to believe or understand."
They added: "Although we now have certain information about how Alice died, we are still left with some serious unanswered questions about what the authorities knew or should have known about the man who is believed to have killed our daughter when he came to the UK."
Alice's Youth Music Memorial Fund, which was set up in her memory, has so far raised £17,000, the family said.
A review hearing ahead of a full inquest into Alice's death will be held at West London Coroner's Court on Thursday.
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