In order for Churchill to write his book, he would have had to study various reports about the occurrence, describing the assassination of the Archduke Franz Ferdinand. Churchill would have had to focus on reports and spoken words from both Gavrilo Princip at his trial and from the crowd who witnessed the event to acquire an accurate description for his book.
The photograph, source 1A, is a secondary source. This is because the Archduke and his wife entered the car twice. The first time, a bomb was thrown onto the car, which bounced off and subsequently the second time, the Archduke was shot. Therefore, since the photograph does not show the assassination it is a secondary source. The photograph is also a secondary source because both the Arc
hduke and his wife are not in the car, where they would be assassinated.
Gavrilo Princip tried to commit suicide because he knew that the police would arrest him and either kill him after the trial or sentence him to life in prison. Princip did not want this and therefore tried to kill himself.