Complex sentence: In 1982, Sánchez participated in a drug bust (seizure of illegal drugs by the police) with his partner which was the beginning of the end of his career as a police officer.
Split into simpler sentences: In 1982, Sánchez participated in a drug bust (seizure of illegal drugs by the police) with his partner. This drug bust marked the beginning of the end of Sánchez's career as a police officer.