My assumption is that the uniform was that of a metropolitan transport service like KVG in Kiel (since he was from Schleswig-Holstein) or Rheinbahn in Dusseldorf. I guess some of these are old enough to exist back in those days.
Unfortunately the Nazis had an obsession with daggers, they were presented for everything imaginable.
The Eagle on the hat definitely isn't military for the Wehrmacht or SS. The collar tabs are similar to the style for the SA who had that dashed border and standarten numbers.
The shoulder boards do seem to be similar to Reichsbahn but the eagles and collar insignia are wrong, one possibility i was thinking is Bahnschutzpolizei but again the collar tabs and hat insignia are wrong.
The jacket has a WW1 look to the collar, the shoulder boards could be Reichsbahn but could also be early version of the SS
The belt and dagger are pure SS style but it has a civilian belt buckle
The hat has a German eagle but it doesnt have the swastika under it but the circular badge could either be the reichbahne wheel or the WW1 army cockade.
The collar tabs are pure SA style with the Standarte number.
The uniform could be either dark blue or black so thats no hint.
The cuff title is unreadable.
If its some sort of early composite SS uniform then Standarte 4 is based in altona, Hamburg which is only an hours drive away from Lubeck.
However, early SA and SS uniforms only used one shoulder board to keep the cross belt in place, if it was one of the Allgemeine SS uniforms where part time unpaid volunteers were assembling their own outfits on a budget that would make sense but he wouldnt have two shoulder boards.