LONDON (Reuters) - Almost a decade after three-year-old Madeleine McCann vanished, London police said they were still following critical lines of inquiry but might never solve the case.

McCann disappeared from her bedroom on May 3, 2007 during a family holiday in Portugal, while her parents were dining with friends at a nearby restaurant in the resort of Praia da Luz.

Despite a massive international search and media coverage which prompted reported sightings from across the globe, her fate remains a mystery.

“Sadly investigations can never be 100 percent successful,” said London Metropolitan Police Assistant Commissioner Mark Rowley. He said police had no definitive evidence as to whether Madeleine was alive or dead.

“We will do everything we can do reasonably to find an answer as to what’s happened to Madeleine. I so wish I could say that we’ll definitely solve it. But a small number of cases sadly don’t get solved.”

Her parents, Kate and Gerry, said the 10-year anniversary was a “a horrible marker of time, stolen time”.

“The two themes that seem most appropriate to me as we reach this ten year mark are perseverance and gratitude: We will go on, try our hardest, never give up and make the best of the life we have,” Kate wrote on their Find Madeleine Facebook web page.

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In the 10 years since McCann vanished, the media has suggested a host of explanations for her disappearance, ranging from a burglary gone wrong to abduction by slave traders.

Madeleine’s parents were named as official suspects by Portuguese police four months after the disappearance but in 2008 were cleared. Portugal’s public prosecutor later dropped the case, citing a lack of evidence.

“There’s no reason whatsoever to reopen that,” Rowley said.

“DOWNRIGHT LIES”

The McCanns and friends who were with them on the night Madeleine went missing later won large payouts from newspapers over stories that they were involved. Another Briton was awarded 600,000 pounds in damages over false allegations he had abducted the girl.

“We are bracing ourselves for the next couple of weeks,” the McCanns said. “It’s likely to be stressful and painful and more so given the rehashing of old ‘stories’, misinformation, half-truths and downright lies which will be doing the rounds in the newspapers, social media and ‘special edition’ TV programs.”

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The Portuguese closed their inquiry in 2008. London police launched a review of the case in 2011 after the McCanns wrote to then British Prime Minister David Cameron.

The subsequent investigation examined 600 individuals and threw up new leads, prompting Portuguese prosecutors to order the case re-opened in 2013.

Following interviews and a search of wasteland near Praia da Luz, four suspects were cleared of any involvement.

London police have spent 11 million pounds on their investigation and last month were given another 85,000 pounds for four detectives to continue for a further six months.

“Where we are today is with a much smaller team focused on a small number of remaining critical lines of inquiry that we think are significant,” Rowley said.

“If we didn’t think they were significant, we wouldn’t be carrying on.”