The main suspect in the Madeleine McCann case rented the allotment being searched by police in Germany, a man who owns a neighbouring plot claims.
The allotment owner told the BBC that the suspect Christian B arrived there in the year Madeleine went missing.
German prosecutors have said the search at the site near Hanover is related to the investigation into Christian B, a sex offender in prison in Germany.
Work began at the site on Monday and is expected to continue until Wednesday.
Madeleine was three years old when she went missing while on holiday with her family in Portugal 13 years ago.
She disappeared from an apartment in Praia da Luz on the evening of 3 May 2007, while her parents were with friends at a nearby tapas bar. It sparked a huge police hunt across much of Europe.
The man whose allotment neighbours the one being searched told the BBC that Christian B rented the plot for a few months in the year that Madeleine went missing.
The man said that Christian B arrived in the spring or summer of 2007 and told him he wanted to insulate a small shack which stood on a concrete base in the garden with a small cellar underneath.
The neighbour went on holiday in July 2007. When he returned in August, he said, the structure had been removed and he never saw the suspect again.
Christian B was revealed as the main suspect in the case in June, as German and UK police made a fresh appeal for help.
Suspects’ surnames are not usually revealed in Germany for privacy reasons.
The 43-year-old is believed to have been in the area where Madeleine was last seen while on holiday in the Algarve in Portugal.
Police said he was regularly living in the Algarve between 1995 and 2007 and had jobs in the area, including in catering, but also committed burglaries in hotels and dealt drugs.
German prosecutors have previously said they have evidence that leads them to believe Christian B killed Madeleine, but it is not strong enough to take him to court.
Last month, the Metropolitan Police said the case remained a “missing persons” investigation in the UK because there was no “definitive evidence” as to whether Madeleine was alive or not.
However, German investigators have said they are assuming Madeleine is dead.
After the latest police appeal, Madeleine’s parents, Kate and Gerry McCann, said: “We will never give up hope of finding Madeleine alive, but whatever the outcome may be, we need to know as we need to find peace.”