Final answer:
During World War II, many Jews in hiding perished in the Holocaust as they were discovered by the Germans and sent to concentration camps. Mr. Frank obtained information about those in hiding from official records and testimonies, and he chose to publish Anne Frank's diary to raise awareness about the Holocaust.
Step-by-step explanation:
During World War II, many Jews went into hiding to evade capture by the Nazis. Unfortunately, most of those in hiding perished in the Holocaust. They were often discovered by German authorities or betrayed by informants. They were then sent to concentration camps and extermination camps.
Mr. Frank obtained this information about those in hiding, including his own family, from various sources. He was able to piece together the fate of those in hiding through official records kept by the Germans, testimonies from survivors, and information provided by the resistance movement. After the war, he collected and published his daughter Anne Frank's diary to share her experiences and to ensure that the world would not forget the atrocities of the Holocaust.