«لَوْ أَنَّ لَنَا مَنْ يَنْطَلِقُ فِي أَثَرِهِ لَأَتَانَا بِفَصِّ خَبَرِهِ»
If only someone could follow him and return with the core of his story.
Faṣṣ khabarihi means the essential account. Al-Ḥārith avoids openly identifying Abū Zayd but suggests learning what happens after his departure.
The judge dispatches a trusted agent. It is a plot event within the narrative, not a general warrant for intrusive surveillance.