The BBC adds from an unknown source that "the remaining line of inquiry is centred around a letter asking for assistance sent from UK investigators to the Portuguese Public Prosecution Service in July 2015".
IIrc this would have been the 6th rogatory letter sent to the Portuguese during Operation Grange. It is mentioned in this article from last year stating:
Nothing is known regarding it's content but if we follow the line of rogatories during this investigation we might be able to see at least which direction it might be heading.However, there is no indication Operation Grange will 'wind down' any time soon.A spokeswoman for the Attorney General's office in Lisbon said the letter was received in July and will be acted on by the Policia Judiciaria, which is running the Portuguese investigation into Madeleine's disappearance in Praia da Luz, on the Algarve, on May 3, 2007.A source on the Portuguese investigation said: 'This letter shows the investigation is still very much alive and that both British and Portuguese police are still working together to try to find out what happened to Madeleine.'The case is not about to be shelved.'
At the beginning we had a long succession of requests for possible suspects to be questioned that came to nothing. We then had the digging excursions that centered on two specific points where the body of Madeleine might have been deposited, initially and possibly at a later point in time. The last rogatory letter we know anything about was the 6th letter that was refered to only in the paper edition of Correio da Manhã on 14 March 2015.:
Scotland Yard has already sent a new rogatory letter in which they request the carrying out of new DNA tests on evidence already analysed in 2007So they had eliminated all suspects and were now concentrating on forensics from 2007, possibly parts of the net curtains from 5A, the boot compartment from the hired car or strands of hair that were still in Portugal.
After this we are now down to one lead left, with one rogatory letter still to go. To me it is a cautiously optimistic message we had today, especially after BHH said that it was basically a Portuguese investigation.
So far Operation Grange has eliminated Jane Tanner's Bundleman, placed Smithman into the center of the investigation with a breathtaking photofit pointing towards a certain person, eliminated every possible perpetrator in the vicinity of Praia da Luz at that time and were then revisiting the crime scene with possible hiding places at locations that were in accordance with specific theories.
Whether this will lead to additional evidence is questionable and with the body still missing there might be an end to the investigation soon, but imo the investigation has reached the point where it is clear where the one lead left is pointing to.
