Research over the years
Explanations for the discovery are mainly based on testimonies, because no documents about the raid on the Secret Annex have been preserved. For a long time, betrayal was considered to be the reason for the arrest of the people in hiding, but the focus is shifting, as there are several other options.
The subject is still being researched. For instance, the Anne Frank House recently reinvestigated the raid, and in 2017 a former FBI officer announced that he would be looking for the possible traitor of the people in hiding with the help of an international cold case team and new technology.