Most likely an adult.
Possibly worked in some sort of government office.
From this analysis and other assimilated knowledge, the team concluded that the author of the note was:
Dutch.
An employee of, or somehow connected to, the Amsterdam SD at the Zentralstelle office in Euterpestraat.
Possibly working directly with or for leading officers dealing with highly classified material. One can assume that only trusted Nazi employees, SD men, Dutch detectives who worked for the SD, and V-persons were able to see or be aware of the kinds of lists mentioned in the note.
Eager to unburden him-or herself of painful information.
Someone who knew or knew about Arnold van den Bergh, since his private address was mentioned in the note.
Looking for a Dutch insider at the Zentralstelle who might fit the operational profile, the Cold Case Team came up with the name of Cornelia Wilhelmina Theresia “Thea” Hoogensteijn. The team had earlier come across her name in the telephone directory of the Amsterdam SD, where she was listed as secretary to Willy Lages and Julius Dettmann.
Born in Germany in 1918, Hoogensteijn moved with her Dutch Catholic family back to the Netherlands when she was nine. By age twenty-four, proficient in both German and Dutch, she got a job as typist at the Zentralstelle. At first, she was translating the Nazis’ anti-Jewish provisions into Dutch, registering Jews during the Razzias, and typing the reports of the interrogations of political prisoners at SD headquarters.2
At face value, her employment at SD headquarters gave the appearance that she was a supporter of the Nazi occupation, but the Cold Case Team discovered that she was on good terms with two Amsterdam policemen who were working for the resistance: Arend Japin and Piet Elias. They would later testify that she was helpful to them and instrumental in securing the release of twenty students arrested to be sent to forced labor in 1943. Psychologically, working as a quasi double agent eventually became too much for her. Appalled by the gross abuse of prisoners at the headquarters, she resigned in early 1944.3 However, the resistance considered her a valuable asset and pressured her to return to work. That June, she was promoted to personal secretary to the dreaded SD chief, Willy Lages. And as the SD telephone directory makes clear, she also became secretary to Dettmann, which means that she very likely could have known about a list made and delivered to the SD by Van den Bergh, as the note suggests.
By the end of 1944, however, the SD began to suspect her of connections to the resistance. Lages typed on her typewriter, “Thea, you are a traitor.”4 In January 1945, she was arrested on suspicion of spying, but without hard proof, she was released after three days. With her cover blown, she immediately went into hiding, with a letter from a member of the resistance vouching for her.
Attempting to cross into the liberated south, Hoogensteijn and her lover, Henk Klijn, were arrested on March 11 and sent to a prison camp near the city of Tilburg. The intelligence officer from the 15th Scottish Division who interrogated her had obviously learned of her past employment with the Amsterdam SD. （It seems that her letter of reference from the resistance carried no weight.） After the liberation on May 5, she was transferred to Fort Ruigenhoek internment camp near Utrecht, where she was held along with more than one thousand other women, mostly wives of NSB members. Devastated, she isolated herself from the rest of the prisoners, refused to eat, and attempted suicide. She was then sent to a mental institution in Utrecht. By the end of August, she was admitted to the Valerius Clinic, a psychiatric hospital in Amsterdam, where she was diagnosed as suffering from hysterical psychosis, and at the end of November, she was given the first of fifteen shock therapy treatments.5
She was finally released on May 21, 1946, but the war had destroyed her life. No longer welcome in her family, who saw her as a moffenhoer （whore of the Germans）， she emigrated to Sweden in 1947 and eventually to Venezuela. It wasn’t until 1960, when a full-page article appeared in a Dutch newspaper with the title “At the SD in the Euterpestraat, Thea Saved Many Lives,” that she was finally praised as a forgotten resistance heroine.6
It is unlikely but not impossible that Hoogensteijn wrote the anonymous note. Had she written it before she was arrested on March 15 and sent it to the Prinsengracht 263 address （she did not have Otto’s name）， Kleiman or Kugler would have opened the letter. However, they did not know anything about an anonymous note. Writing it later from one of the internment camps, she would probably have had to use special stationery, and Otto would have mentioned it. By the end of August, it would seem, she was in no state to write such a letter. Unfortunately, although Otto told Detective Van Helden that he had received the note shortly after liberation, he did not disclose the exact date. In the end the team concluded that the note, if not written by Thea, was very likely written by someone with inside knowledge of the workings of the SD. But just as they were preparing to investigate further theories of its authorship, they became distracted by something that would turn out to be even more important: reasons to believe in its contents.