And Detective Inspector Jon Cousins revealed that an item in Ben’s possession around the time he went missing was found on Saturday at one of the search sites near his family’s farmhouse.
Mr Cousins said he had shown the item to Ben’s family, who were left “distraught” at the discovery.
South Yorkshire Police’s three-week digging operation on Kos in a bid to solve the mystery of Ben’s disappearance 25 years ago came to an end this weekend.
In a press conference this afternoon, Mr Cousins said that in the last 19 months detectives “have closed off a large number of theories about what happened to Ben, many of which have been open for over 20 years”.
He said: “However, based on the information that I have now, as a result of an extensive and thorough investigation, it is without doubt that the current line of enquiry is the most probable cause for Ben’s disappearance.
“My team and I know that machinery, including a large digger, was used to clear an area of land on 24 July 1991, behind the farmhouse that was being renovated by the Needham’s. It is my professional belief that Ben Needham died as a result of an accident near to the farmhouse in Iraklis where he was last seen playing.
“The events leading up to and following that incident have been explored by my team of experts to great lengths. The fact that we have not had a direct result during this visit to Kos does not preclude the facts that we know to be true.
“An item found on Saturday, which I have shown personally to some of Ben’s family, was found in one of the targeted areas at the second site, very close to a dated item from 1991.
“It is our initial understanding that this item was in Ben’s possession around the time he went missing.
“The recovery of this item, and its location, further adds to my belief that material was removed from the farmhouse on or shortly after the day that Ben disappeared.
“Ben’s family have been provided with a full and thorough account of the events which we know to have taken place and also the speculations that we have been able to discount. Our thoughts are with the family as they are given time to digest this and they have our full and continued support.
“Our drive has always been the family, and their welfare. Ben’s family have never given up on the team and I am incredibly thankful for their constant inspiration.
“We are also grateful to the current Greek authorities for their assistance, and the help received from the Home Office and the Foreign and Commonwealth Office has been vital in allowing the team to continue getting answers for a family in need.
“We remain committed to the investigation and it will not simply close; myself and Detective Superintendent Matt Fenwick will retain ownership of it and if new information comes to light, we will investigate it thoroughly. We will not stop in our quest to find further answers for Ben’s family.”
Over the weekend, Ben’s mother Kerry collapsed and broke down in tears at the spot where her son disappeared 25 years ago.
Kerry Needham, 44, visited the location on the Greek island of Kos where Ben was last seen alive, after police officers from South Yorkshire called off their search of the area.
They had spent nearly three weeks excavating two sites on the island, with detectives working on the theory that Ben may have been crushed and buried by a digger.
Ben, who was 21 months old when he vanished, was playing outside a farmhouse his grandfather was renovating when he went missing in July 1991.
A digger was clearing a building plot nearby and it is believed that Ben may have been accidentally crushed.
South Yorkshire Police said on Sunday that the excavation work at two sites of interest had finished.
Ms Needham said she wished she could “tear up the whole island to find him”.
She added: “I can’t say goodbye until I know where he is.”
Accompanied by her parents, Christine and Eddie, she laid flowers at the spot where Ben was last seen and urged anyone with information to come forward.
“They know he’s dead but just can’t find him,” Ms Needham said.
“Police said it’s time we ended our 25-year search. They are right but I can’t say goodbye knowing he’s still on that island somewhere. I feel physically sick. I can’t feel any worse than I do.
“Somebody knows where he is. Somebody else put him there and I can’t say goodbye until I know exactly where he is. Please let me say goodbye to my son. I can’t leave him there on that island. I need to find him. I need to take him somewhere he can be at peace and I can be at peace and grieve for him and somewhere I can remember him.”
Ben’s family had always believed he had been abducted until police received information in June suggesting he may have been accidentally crushed and buried.