I managed to fix it, so it works now.
I used sewing machine oil and a piano wire to work the pins. It is 5 pins, not 6 as a suspected. After that we felt sure that the lock actually was open but jammed on the outside of the cyliner and impossible to twist. So I used a small pincer to force the key. And finally it open.
I used sewing machine oil and a piano wire to work the pins. It is 5 pins, not 6 as a suspected. After that we felt sure that the lock actually was open but jammed on the outside of the cyliner and impossible to twist. So I used a small pincer to force the key. And finally it open.

