VALLETTA (Reuters) - The Maltese government’s former chief of staff has been arrested and faced a second day of questioning on Wednesday as part of an investigation into the murder of journalist Daphne Caruana Galizia, police sources said.

Keith Schembri, a close friend of Prime Minister Joseph Muscat, resigned on Tuesday after he was named by businessman Yorgen Fenech as a “person of interest” in the investigation, the sources said.

The police have not officially said why Schembri was under arrest or whether he was considered a suspect in the case that has rocked Malta and led to renewed calls by opposition politicians for Muscat to resign.

Neither Schembri nor Fenech have made any public statement since their arrests and their lawyers have not responded to requests for comment.

Fenech was detained a week ago as he tried to leave Malta on his yacht, the day after news broke that the suspected middleman in the 2017 murder of Caruana Galizia had been arrested.

Caruana Galizia was killed by a car bomb as she drove out of her home. Three men are awaiting trial for having set off the bomb.

The suspected middleman, Melvin Theuma, was granted a presidential pardon on Monday in return for evidence that could be used in court to convict those suspected of ordering the killing. Local media reported that he had handed over audio recordings.

Slideshow ( 10 images )

Caruana Galizia’s family said they wanted a meeting with Malta’s attorney general, Peter Grech, to discuss media reports that Fenech may also be given a pardon in return for naming senior officials who were complicit in ordering the killing.

“We urgently want to clarify the situation,” said Paul Caruana Galizia, one of Daphne’s sons.

The Times of Malta newspaper reported on Wednesday that Fenech’s doctor had also been arrested on suspicion that he passed messages from Schembri to Fenech following his arrest last week, urging him to keep quiet.

The police have 48 hours within which to either charge or free people under arrest but Fenech has been arrested and released three times in quick succession as questioning and investigations continue.