As of 2014, no one has conclusively determined who betrayed Anne Frank. Two official inquiries by Amsterdam police have been performed, and substantial research and speculation has been done by Frank family biographers and historians as well. Several suspects have been named, but no suspicions have been proven.
For many years, stockroom manager Wilhelm van Maaren was the primary suspect. Dishonest and inquisitive, van Maaren aroused suspicion by keeping an eagle eye on those who entered and exited the stockroom and by asking leading questions about former employees, including Otto Frank. While he was thoroughly investigated, no solid evidence that he was the betrayer was ever uncovered.
Lena van Bladeren-Hartog, who worked as a cleaner at the premises and whose husband worked in the stockroom, also emerged as a suspect, but little substantive evidence was found to support the suspicion. Tonny Ahlers, a notorious anti-Semite with Nazi affiliations, has also been named and explored as a suspect.
Miep Gies, the woman who, along with her husband Jan, helped hide the Frank family in the attic, was of the opinion that the identity of the betrayer would never be known. She reported in interviews that the officer who initially made the arrest did not know who had called, and the Nazi who had taken the call died before revealing his source.