Complex sentence: After working closely with the FBI, TheBritish Anti Terrorist Branch, Special Branch and The Crown Prosecution servicehis expertise was so valued that he was the chief prosecution witness in the world's first ever post September 11th al Qaida terrorist trial.
Split into simpler sentences: After working closely with the FBI, The British Anti Terrorist Branch, Special Branch and the Crown Prosecution service. His expertise was so valued that he was the chief prosecution witness in the world's first ever post September 11th al Qaida terrorist trial.