を追跡した

tracked

→ を
phrase Rare #42,330
tracked 追跡した is the past tense of 追跡する, meaning “to track” or “to pursue.” The particle を marks the person or thing being tracked. In the examples, the phrase appears with different forms such as 追跡している and 追跡して下さい.
JA: 警察は逃げた車を追跡した。
EN: The police tracked the car that fled.

刑事たちはを追跡した

The detectives tracked him down.