VALLETTA (AFP) - Maltese Prime Minister Joseph Muscat said on Tuesday (Nov 19) he had promised the alleged middleman in Ms Daphne Caruana Galizia's murder a pardon if he identifies the mastermind of the journalist's assassination.

Mr Muscat made the surprise offer after authorities on Thursday arrested someone who claimed to know who ordered the deadly 2017 car bombing of the renowned blogger and journalist.

The pardon would cover any criminal cases the suspect may face, but he must assist the authorities and his evidence must be corroborated in court, Mr Muscat said.

Maltese police and Interpol, which has been helping with the high-profile case, last week arrested several people as part of an anti-money laundering operation, including someone suspected of involvement in Ms Caruana Galizia's murder.

Ms Caruana Galizia, described by supporters as a "one-woman WikiLeaks", had highlighted corruption in Malta, including among politicians.

"The targeted person, following interrogation, expressed the intention to collaborate with the authorities and through his lawyers requested that first a presidential pardon be given on all the cases he might have had," Mr Muscat told journalists.

"I have discussed the issue with the authorities including the attorney-general and we agreed that no blanket pardon should be given without any certainty regarding the information to be submitted."

"I have signed a letter... that states that when the person testifies in court and the information is confirmed and corroborated, I would be recommending that this person is granted a presidential pardon," Mr Muscat said.

Mr Muscat and his family were among those accused by her investigations and her blog, which often launched highly personal attacks.

Three men are facing trial for allegedly carrying out the killing, but the mastermind has not been identified.

In September, Malta made a surprise U-turn and appointed a retired judge to head a public enquiry into the journalist's 2017 killing.