VALLETTA, Malta — A prominent Maltese businessman has offered to testify against top government officials over the 2017 murder of the journalist Daphne Caruana Galizia, and said the prime minister had a conflict of interest in the case.

The businessman, Yorgen Fenech, was arrested last week in connection with the killing. Lawyers for Mr. Fenech on Thursday deposited in court a letter to President George Vella formally asking for a pardon.

In return, Mr. Fenech promised to supply information related to the former government chief of staff Keith Schembri, former Tourism Minister Konrad Mizzi, Economic Affairs Minister Chris Cardona and other people “close to the prime minister.”

The lawyers for Mr. Fenech said Prime Minister Joseph Muscat should not be involved in deciding the plea for a pardon, because he was among “persons who may have an interest for such a pardon not to be granted.” They also called for removal of chief investigator Keith Arnaud, claiming he was close to Mr. Schembri.