There is nothing at
http://luftwaffe-zur-see.de/Seeluft/...n/Jahr1940.htm.
Two death cards exist on fold3 for Erich Bohlmann, and one each for the other two men. All confirm the place given by Matti, and say it occured at 0845 hrs and it was an accident '"Unfall") but no more details. While reading the first card, I thought the last barely readable sentence could be death details, but actually they are only say where the dead was sent (probably in family cemetery).
Seeing KG 4 members being allocated to a Luftwaffe "maritime school" in February 1940, I wonder if they were not preparing for support of the invasion of Norway ?