Wow, that was fast! Thank you so much. I found its set (6816 Cyber Blaster), rebuilt it but it turns out that I still have some left-over parts which probably belong to another set. Especially the Octagon seem to me as a unique part which shouldn't have made many appearance in set. How can I filter in which sets the parts has made it?
BrickLink - Part 30033 : Lego Plate, Modified 2 x 2 with Bar Frame Octagonal [Plate, Modified] - BrickLink Reference Catalog
Edit: I found the solution: under "Item appears in" in the top right section, next of the picture.