question about the being shot down

According to Wikipedia, it seems that it's possible the Soviet Union thought he had information that could harm them. We weren't in the war yet, something I hadn't remembered, so they didn't know what to think of us. Here's what I just found:

Antheil, younger brother of noted composer George Antheil, was a clerk at the U.S. legation in Helsinki. He was killed on June 14, 1940, while serving as a diplomatic courier when the Finnish passenger plane Aero Flight 1631 was shot down over the Gulf of Finland near Tallinn, Estonia, at 14:05, approximately ten minutes after taking off from Tallinn Airport.[2]

Two Soviet bombers downed the passenger airplane on the day the Soviet blockade of Estonia went into effect.[1] According to an Associated Press wire story that ran the following day, Antheil was serving as a diplomatic courier when his plane exploded en route to Helsinki.

Antheil was carrying several diplomatic pouches from the U.S. legations in Tallinn and Riga. Soviet troops had already been based in Estonia since October 18, 1939, as a result of the secret protocol to the Molotov–Ribbentrop Pact signed between the Soviet Union and Nazi Germany. Some Estonian researchers believe that Antheil's diplomatic pouches included secret information detailing the Soviet Union's future plans for the Baltic region that the Estonian General Staff had turned over to an unidentified U.S. government official earlier that same day. Back in the United States, the news of the Soviet blockade and the loss of the Aero Flight 1631 were overshadowed by a much bigger story that broke on the other side of Europe on June 14: the German occupation of Paris.[3]