Police in London have asked the United Kingdom's Home Office for more funding to continue the investigation into the disappearance of Madeleine McCann, the girl who went missing May 3, 2007. Authorities have spent around $13 million investigating Madeleine’s disappearance.

A search unit, named Operation Grange, was formed at the request of David Cameron’s government in 2011 after a plea from Madeleine’s parents. It last received more than $210,000 extension in September 2017. A team of four Met police detectives continued to investigate Madeleine’s disappearance after the number of officers on Operation Grange was reduced from 29 in October 2015. 

"The Home Office has provided funding to the Metropolitan police for Operation Grange and the resources required are reviewed regularly with careful consideration given before any new funding is allocated," a Home Office representative said in a statement.

Madeleine went missing after her parents left the 3-year-old and her 2-year-old twin siblings alone inside a vacation apartment rental in Portugal in 2007 while they went out to dinner. Her parents, Kate and Gerry McCann, maintained their innocence in relation to their daughter’s disappearance. They were named as official suspects four months after her disappearance, but Portuguese police dropped the case in July 2008 due to lack of evidence. 

In May last year, on the 10th anniversary of Madeleine’s disappearance, police said over 600 individuals were investigated and 40,000 documents reviewed in relation to the case. Kate and Gerry McCann, Madeleine’s parents, have said they will never give up hope of finding their daughter.

“Right now we are committed to taking the current inquiry as far as we possibly can and we are confident that will happen. Ultimately this, and the previous work, gives all of us the very best chance of getting the answers – although we must, of course, remember that no investigation can guarantee to provide a definitive conclusion,” Met police said last year.

In November, reports surfaced about a person of interest in the case, said to be a "woman in purple" who may have information about the Madeleine.

“Because it’s worth pursuing, it could provide an answer,” Metropolitan Police Assistant Commissioner Mark Rowley told the Press Association at the time. “But until we’ve gone through it, I won’t know whether we are going to get there or not. We’ve got some critical lines of inquiry, those link to particular hypotheses.”

It remains unclear whether Madeleine was alive or dead. The young girl's parents remain hopeful as the search for their daughter continues and police ask for additional funds to carry out the investigation. They were reportedly "encouraged and extremely grateful” that detectives are still determined to solve the mystery.

"This remains entirely a matter for The Met Police and Home Office," family representative Clarence Mitchell said, according to the Sun. “But Kate and Gerry are extremely grateful to police for all they have done and are doing in the continued search for their daughter."