These claims have not been sufficiently substantiated
1. The people in hiding were betrayed.
In the autumn of 1945, Otto Frank wrote to family members that he and his helpers were trying to find out who had betrayed them.
They were convinced that they had been betrayed. It is understandable; many people fell into German hands during the occupation and this was often because they had been betrayed. However, there is no concrete evidence that this was the case here.
For a long time, research pivoted around betrayal as the cause of the arrest. Below, you will find a number of theories that were researched within the context of this scenario, but that were not sufficiently substantiated to be accepted.
1a The SD received a tip-off by phone about the Secret Annex which was the cause of the raid.
It has never been proved and can no longer be proved that on 4 August 1944 someone called the SD to betray the people in hiding.
The story of such a phone call, supposedly made in the morning of August 4, came from SD-officer Silberbauer. Nazi hunter Simon Wiesenthal tracked him down in 1963 and in his first written statement Silberbauer only mentioned "a Dutchman" as the caller.
However, his statements were not consistent. At a later date he claimed that he was not sure whether a phone call had been made, nor who had made it. According to a journalist at De Telegraaf, Silberbauer said that the call had been made by warehouse worker Willem van Maaren. But that is not very reliable either: in the summer of 1944, private telephone communications were all but down, due to large-scale disconnections. As a result, regular citizens would have had limited opportunity to place such a call.
1b A woman called the SD and betrayed the people in hiding
According to another story, the SD officer who took the alleged call said that he had spoken to a woman.
This officer, Julius Dettmann, died in his cell a few weeks after the liberation. Silberbauer stated that Dettmann never told him who had made the call. The story about the female voice came from someone who allegedly told Otto Frank about it. However, there is no evidence to this effect.
1c Willem van Maaren was the traitor
The helpers did not trust warehouse worker Willem van Maaren. The people in hiding shared their suspicion, without knowing him or even having seen him. Anne wrote about it in her diary and attributed negative qualifications to him.
In 1947, Otto Frank and the helpers filed a complaint against him with the political police on suspicion of betrayal. However, the investigation did not prove his guilt. Van Maaren fought the accusations and rejected a settlement. The Subdistrict Court dismissed the complaint. A new investigation followed after Silberbauer had been tracked down. It yielded new information but still no evidence against Van Maaren.
1d Tonny Ahlers was the traitor
Tonny Ahlers was a Dutch national socialist. When he found out that Otto Frank had expressed a negative opinion about the German war chances in a conversation in the street, Ahlers pressured Frank and extracted money from him.
In her biography of Otto Frank, Carol Ann Lee suggested that Otto Frank supplied the German army with goods during the occupation. According to her, Ahlers played a role in the transactions because he had a hold over Frank and later betrayed the people in hiding in the Secret Annex to an SD detective. However, the only verifiable delivery was very small in size and there is no indication that Ahlers knew about people in hiding in the Secret Annex.
1e Lena Hartog was the traitor
Lena's husband Lammert did undeclared work in the warehouse at Prinsengracht 263. He spoke with his wife about people hiding in the building. However, it was never clarified whether he did so before or after the arrests on 4 August. If he did so after that day, that would hardly be surprising, for Lammert witnessed the raid. There is no indication that he had known of their presence before.
Lena talked to a friend about the people in hiding. This woman was shocked. If this was after 4 August, that is understandable. She knew Kleiman, who had by then been interred, and rumours could compromise third parties around him.
The theory that Lena spoke about the people in hiding before 4 August and may even have been the woman who called the SD, was first suggested by Anne Frank biographer Melissa Müller. However, there is no evidence to support this theory.