Tanbark Borer Violet Beetle

Moved to Arthropods category

A type of longhorn beetle. This species comes in many different colours. The source I linked features a specimen that is the same colour as yours. (auf Deutsch: Variabler Schönbock)
Warning: these things eat through wood and are the reason why some old, wooden houses collapse. So I hope you did not find it anywhere near some wooden, structurally important parts of your house!