Following a light breakfast of toast and coffee, the two men headed off in opposite directions to continue the search. Vargas only had a five-minute walk to the city hall and, after a protracted conversation with a highly disagreeable front-desk clerk, he eventually found himself in the housing records department. The young woman in charge was clearly impressed by the credentials of the chief inspector from the Buenos Aires Police Department and was eager to help. None of the property records had been digitised and the original paperwork lay in hundreds of boxes piled on top of each other in a large basement stockroom.

They all had handwritten dates on the side and, after a fifteen-minute search, she located the one dated June to December 1945.

She placed it on the large desk in front of Vargas and opened the lid. The box only contained four documents.

“Quiet times back then, chief inspector. Not many houses were bought or sold.” She flicked through the small pile of papers, then pulled one out and handed it to Vargas.

“Here you go, El Blondi. A newly built property, first registered on 10 June 1945. The owner was Gerald Franklin.”

Vargas felt like he’d found the holy grail as he held the original document in his hand. He took a photo of it with his iPhone camera and passed it back over to the records clerk. “How do we find out when it might have been sold to a new owner, or maybe developed into a block of flats? There doesn’t seem to be any sign of a property called El Blondi anywhere in the city.”

“I’m afraid there is no way of cross-checking, other than going through every box until you find a relevant transaction and, as you can see, there are a lot of boxes.”

Vargas sat back in his chair and cursed under his breath. He thanked her and made his way to the door, bracing himself for a long walk around the west of the city.

Then an idea formed. He took out his mobile and flicked through his photo library until he found the death certificate of Emilia Franklin, aka Eva Braun. It recorded the death as 28 October 1970. He spun round and called over to the records clerk, who was busy lifting up the 1945 box from the table. “Can I see all the records between October and December 1970, please?”

After sifting through over thirty property sales documents, Vargas found what he was looking for. On 1 December 1970, the property known as El Blondi was sold to a woman named Valentina Suarez and the title of the property was changed. The document also provided a street name. Stapled to the property registration form was a set of architect’s drawings that indicated that the new owner had applied for plans to rebuild the property.

Vargas was ecstatic at the find and thanked the young assistant for her help before reaching for his mobile. He speed-dialled Hembury, who picked up immediately.