Complex sentence: Carl is violent, and burns Ian's hand when he tries to refuse to pay him before promising that the debt will be paid if Ian lies in court, and says that he saw Max tampering with the brakes of Carl's car.
Split into simpler sentences: Carl is violent, and burns Ian's hand when he tries to refuse. Carl then promises that the debt will be paid if Ian lies in court, and says that he saw Max tampering with the brakes of Carl's car.