UFO Sighting in Dresden, Sachsen on 2017-06-24 15:36:00 - The object let a vapour trail that stopped suddenly, after 10 minutes an object appears in the sky

I swas sitting at the balcony and watched a plaine with 4 vapour trails, when i saw 2 metallic objects appeared behind it, could be seen for only 3 seconds and disappeared. i get my camera and focused in to the sky at the place. lens 300 mm, apsc sensor, sony alpha 77. suddenly a single vapour trail eppeared and because this is very unusual (planes have got 2 or 4)i take a picture (picture1) the trail stopped within a cloud. ten minutes later it blows up to a giant dimension and inside an polygone-shaped extreme white object was to be seen (picture 2). minutes later all disappeared. what was unnormal: the single vapour trail, its suddenly stopping, the blowing up into a big dimension (this could not be seen in the case of all planes i watched before and after the event. the vapour trails vanished normally in seconds, depending from the air conditions at this day. the extremly white object that appeares in the blown up vapour trail i had never seen a comparable object in the sky. because i couldn' t take some pics from the other 2 objects that was near the plane (it had no vapour trails), visible only for seconds, it's worthless to mention. only pictures are documents for events. ps: all pictures are taken by the same lens-setting: 300 mm