Final answer:
The correct preterite verb to fill in the blank is 'perseguiste'.
Step-by-step explanation:
The correct preterite verb to fill in the blank in the sentence is perseguiste. The sentence should read: La policía perseguiste al ladrón. The verb perseguir means 'to chase' or 'to pursue' in English. In this context, it indicates that the police chased or pursued the thief.
Learn more about Spanish verb conjugation