Complex sentence: Dasch angrily repeated his story after he was dismissed as a crackpot by numerous agents until he dumped his mission's entire budget of $84,000 on the desk of Assistant Director D. M. Ladd.
Split into simpler sentences: Dasch angrily repeated his story after he was dismissed as a crackpot by numerous agents. He finally convinced the FBI by dumping his mission's entire budget of $84,000 on the desk of Assistant Director D. M. Ladd.