As nature gradually swallows up the crumbling concrete walls of a little-known Nazi concentration camp built on a British island, researchers are digging through records to examine how many people died there during the nearly five years of German occupation.

The Channel Islands, which lie just off the coast of France, became possessions of the English crown around a thousand years ago. When Germany invaded France in 1940, the British government calculated that the Channel Islands had no strategic value and gave them up without a fight. German troops set up two concentration camps, as well as labor camps, on the island of Alderney.

While the British military investigated the camps after the war ended in 1945, the number of deaths there have been hotly disputed in the decades since. The British military put the death toll in the low hundreds, but amateur historian Marcus Roberts, who’s spent years researching this forgotten chapter in British history, argues more than 10,000 must have died on Alderney. Roberts said his Jewish heritage has made him determined to count all of the dead.

“There is the Jewish instinct to, you know, leave no one behind,” he said.

What happened on Alderney 

Nearly all of the residents of Alderney, an island about three miles long and one-and-a-half miles wide, decided to evacuate before the German troops arrived. The troops brought in prisoners of war and forced laborers to build giant fortifications — part of Hitler’s Atlantic Wall to protect against Allied attack — that still stand today. A minority of the prisoners were Jewish. Others were from Russia, Ukraine, Poland, Spain and other European countries. 

“So, undoubtedly, if you wanted to put a pin on the map, you could say, ‘This is where the Holocaust happened on British sovereign territory,'” Roberts said.

One prisoner testified, “We were beaten with everything they could lay their hands on: with sticks, spades, pickaxes.”

There’s no evidence that gas chambers were used on Alderney, but there were summary executions, Dr. Gilly Carr, an archaeologist at Cambridge University, said. Prisoners built the Nazi fortifications on starvation rations.

“They were certainly seen as expendable,” Carr said. “The aim was to get every ounce of work out of them. And if they died, it didn’t matter, and that was kind of, perhaps, ‘expected.'”

According to prisoner statements, some people were dumped at sea or thrown off cliffs. It’s part of the problem when it comes to determining how many have died. 

“It is likely that some of the people in mass graves were Jewish. And according to Halakha, or Jewish law, you cannot disturb the dead,” Carr said about the other reason for the document-focused approach.

What happened on other parts of the Channel Islands?

While nearly all the residents of Alderney evacuated before the occupation, people living on the other Channel Islands chose to stay. The locals mostly cooperated when the Germans arrived — often with little choice. Hitler’s portrait was hung outside a cinema on the island of Guernsey. Nazi propaganda showed the British police working for German troops. A British newspaper on Jersey depicted the swastika and printed orders from Berlin

At the official archives on the island of Jersey, Linda Romeril showed how British officials implemented Nazi policies, asking Jewish residents to identify themselves and then confiscating their assets.

Some resisted, risking punishment to paint anti-Nazi graffiti and illegally listening to British news on the radio. Louisa Gould, one member of the resistance, hid an escaped Russian prisoner in her home for nearly two years, relative Jenny Lecoat said. Lecoat said when her great aunt was finally caught, she was sent to Ravensbrück concentration camp in Germany and was killed in a gas chamber.

While her great aunt was not alone in resisting the Nazis, others “betrayed their own country,” Lecoat said. It created what she described as a “confusing, messy, dirty mixed picture of the Channel Islands occupation.”

“The British government, I think, were kind of ashamed,” Lecoat said. “They were horrified it had happened, and they didn’t really want to get too involved in what had gone on there.”

Was there a cover-up?

It has taken nearly 80 years for the British government to reexamine what happened on Alderney and to make its report public. The official British investigations in 1945 were classified for decades. And unlike the trials of Nazi officials in Nuremberg, the British authorities failed to prosecute a single German officer who worked on Alderney — even though many of them ended up in British prisoner of war camps.

It’s led Roberts and others to claim that the British government tried to cover up the extent of the atrocities on Alderney. Roberts and others believe more than 10,000 must have died on the island based on controversial calculations about the size of the labor force needed to build the fortifications.

Carr said it’s possible that there was a cover-up, but a key document from the British War Office investigation that may explain why there were no prosecutions is missing; she said she has no idea where it is or what happened to it. 

“In order for me to say there was a cover-up, I want to see the decisions taken,” Carr said. “I want to look through those steps and to make up my own mind.”

Why might the British government have tried to cover up or whitewash what happened on Alderney and, more broadly, on the Channel Islands?

“There are some things that happened that might not, that the British government might not necessarily have wanted a wider audience to know about,” Carr said. 

Roberts, for his part, is looking for some kind of an apology from the government. 

“I think it would be appropriate for them to recognize what should have been done, didn’t happen,” he said. 

Why they’re reviewing what happened on the Channel Islands now

Most academics dispute Roberts’ estimate of the death toll, but partly as a result of those disagreements, the British government appointed a team of researchers last year to comb through archives across Europe and more accurately count the number of prisoners who died on Alderney. Carr is coordinating the review. Their report on what happened on the Channel islands during the Holocaust is set to be published on May 22.

They’re drawing on rich material; the Nazis were meticulous record keepers and British archives contain first-hand testimonies from survivors. 

The British government’s effort to get the truth out by re-counting the dead was commissioned by Lord Pickles, a former Cabinet minister and now the U.K.’s envoy for post-Holocaust issues.

“The figures vary, not by a few hundred, not by a few thousand, [but] by tens of thousands,” Pickles said. 

He’s also asked researchers to put names to as many of those killed as possible.

“If you remember them as individuals, then it’s another blow against Hitler,” he said. “Hitler wanted to eradicate the memory of people.”

Holly Williams

Holly Williams is a CBS News senior foreign correspondent based in the network’s CBS London bureau.