in case the date you are referring to is July 1932, Johannes' death may have to do with the "Altona blood Sunday", a confrontation of Nazis, communists and the police, which ended up in 18 people dead.
If so, there should be enough newspaper reports about the event.
Great, thank you very much. I had not heard of this incident. I'll look to see if I can find out more.
PS Yes, my mistake ! The date is 1932.