That’s a great question, and it touches on one of the most subtle mysteries in The Day of the Jackal.

Here’s the key detail: The Jackal didn’t just steal Charles Calthrop’s name at some later point—he had likely been using it as a cover for some time before the events of the novel. The confusion arises because the British authorities (and the reader) don’t initially know this.

Breaking It Down:

    The Dominican Republic Assassination & Calthrop’s Name

    The MI6 officer recalls a rumor that a British assassin named “Charles Calthrop” was involved in a killing in the Dominican Republic.
    This rumor was based on an actual event, but we don’t know if the real Charles Calthrop was ever involved.
    It’s possible that the Jackal had already been using Calthrop’s name as an alias at that time.

    The Real Charles Calthrop

    The novel confirms in the epilogue that the actual Charles Calthrop was never the assassin and had nothing to do with any of this.
    He was in the Dominican Republic at some point, but we don’t get enough details about his movements.
    The Jackal may have stolen or borrowed his identity at some point before or during this period.

    How Did the Jackal Get the Name?

    The Jackal was an expert in forging identities, so he might have gotten access to Calthrop’s details through some means (stolen documents, false passport, black market connections).
    Alternatively, he may have deliberately chosen Calthrop’s name because he knew Calthrop was traveling abroad or was in a location where it would be difficult to track the real man.

What This Means:

The intelligence agencies assumed “Calthrop” was the Jackal because the name was linked to an assassination.
In reality, they were chasing the wrong identity because the Jackal had already been using a stolen alias.
The revelation in the epilogue—that the real Calthrop is alive and uninvolved—proves that the entire manhunt was based on a false lead.

The Big Twist:

The Jackal’s true identity is never discovered. The name “Charles Calthrop” was just another mask he wore, and in the end, he remains an enigma. Forsyth leaves us with that final ambiguity—who was he, really?

Hope that clears things up! What do you think? Does this explanation fit with your reading?