Complex sentence: On July 25,1934 he unsuccessfully tried to prevent Dollfuss' assassination by Otto Planetta, he testified at the trial of murderers as a witness for prosecution (Crown Witness) and was awarded Gold medal of merit by Austrian government for his heroic efforts.
Split into simpler sentences: On July 25,1934 he unsuccessfully tried to prevent Dollfuß's assassination by Otto Planetta. He testified at the trial of the murderers as a "Crown" (prosecution) witness and was awarded the Gold Medal of Merit by the Austrian government for his heroic efforts.