Maltese Prime Minister Joseph Muscat said he has offered an official pardon to the suspect if his evidence leads to the arrest of the mastermind behind the Oct. 16, 2017, assassination of Daphne Caruan Galizia.
The suspect has "indicated they were in possession of evidence to corroborate their information," Muscat said.
Three people were arrested in December 2017 on suspicion of triggering the powerful car bomb that killed 53-year-old Caruana Galizia, but the trial has not yet begun. The mastermind also has yet to be identified.
The arrested suspect is alleged to have acted as a middleman between whoever ordered the assassination and those who carried it out. Muscat said any immunity would require "assurance that the things this person could say could be corroborated in court."
The suspect, who has not been identified, was arrested last week in a crackdown on money laundering and is being held under police protection.
Caruana Galizia's reporting targeted all the political elite in this small European Union nation with the same sense of moral outrage, accusing the country's politicians of corruption and undermining its democratic institutions.
Prior to her slaying, Caruana Galizia had reported receiving threats to police. Her reporting included examining Malta content in the leaked documents in the Panama Papers financial scandal.