Duc had years of experience in France, which had given him a good feel of how the French might be thinking and what their relations with Francophile members of the ARVN might resemble. He used this to concoct some plausible sounding and incriminating documents for Mậu.
Duc's familiarity with France, gained through years of experience, provided him with insight into the French way of thinking and allowed him to anticipate how they might interact with fellow Francophiles within the ARVN. He then used this knowledge to create convincing yet damaging documents for Mậu.