PORT-AU-PRINCE, Haiti — They examined the bodies of Haiti’s slain president and of the mercenaries who are accused of conspiring to kill him. Now they are in hiding, changing their location every few hours, with a backpack full of legal documents that could determine the fate of Haiti’s most important trial in decades.

A judge and two court clerks who collected evidence for the investigation into the killing of President Jovenel Moïse said in interviews and in formal complaints to the prosecutors’ office that unknown callers and visitors had pressured them to modify witnesses’ sworn statements. If they failed to comply, they were told, they could “expect a bullet in your head.”

Their requests for help from the authorities were ignored, said the clerks, Marcelin Valentin and Waky Philostène; and the justice of the peace, Carl Henry Destin, leaving their lives at risk.

The threats also further jeopardized an investigation that experts claim had been marred from the start by irregularities — and which many Haitians fear will not reveal the truth about the killing, despite vows by the country’s current leaders to enact swift justice.

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