On the morning of 6 March 1952, photographer Esse Jansson observed two bright objects in the sky near Norrtälje.

This case matters because it is a documented physical event whose object identity remains unresolved.
Documented
On the morning of 6 March 1952, photographer Esse Jansson observed two bright objects in the sky near Norrtälje.
Debated
The identity of the object
Debated
The adequacy of the conventional explanation
Unverified
Extraterrestrial origin
Unverified
Any claim stronger than the record supports
Sources are kept in separate layers: official and contemporary material is documented; secondary UFO literature is treated as debated, not as primary evidence.
Documented source.
Documented source.