Open this photo in gallery In a TV address on Dec. 1, 2019, Maltese Prime Minister Joseph Muscat said he would resign after a new party leader is chosen. The Associated Press

A week of political turmoil in Malta related to the investigation into the assassination of journalist Daphne Caruana Galizia ended on Sunday night with the announcement of the planned resignation of Prime Minister Joseph Muscat.

In a TV address on Sunday night, local time, Mr. Muscat said he would leave after a new Labour Party leader is chosen, a process that will begin in mid-January. His departure means he is leaving two years short of his full second term.

The resignation was widely expected, although the timing wasn’t known until he made his statement. The announcement of his departure came after a week of high political drama and nightly protests by thousands of Maltese, who demanded he leave immediately to give a fresh start to an investigation they say was harmed by cover-up, conflicts of interest and delay tactics.

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“I promised justice in the case of Daphne Caruana Galizia,” he said. “I kept my word. We have three people charged with her murder and we also have the alleged mastermind.”

He was referring to Saturday’s arraignment of Yorgen Fenech, the Maltese businessman who was charged with conspiracy in the murder of Ms. Caruana Galizia. Mr. Fenech pleaded not guilty. Two months after her murder in October, 2017, three Maltese men where charged with planting the car bomb. They all await trail.

Earlier on Sunday, Mr. Muscat’s ruling Labour Party said it gave its “unanimous support” to the Prime Minister in spite of high-level government resignations tied to the investigation into the assassination of Ms. Caruana Galizia. Her death triggered an intense campaign by her family and civil society groups for speedy justice, which they said was not delivered.

Open this photo in gallery Thousands of Maltese turned out on Sunday to protest the handling of the investigation into Ms. Caruana Galizia's murder. The Associated Press

Sunday night saw the biggest protest of the week. It was organized by human rights and democracy groups such as Repubblika, which gained strength and authority after Ms. Caruana Galizia’s murder.

The protesters shouted “mafia” and “assassins” and carried signs that said “criminals" and “You betrayed your own people.” At one point, fake €5,000 ($7,300) notes fluttered through the air with the faces of Mr. Muscat, his chief of staff, Keith Schembri, and Konrad Mizzi, the former tourism minister, printed on them – a reference to alleged kickbacks from an opaque government energy contract Ms. Caruana Galizia had written about.

Mr. Schembri resigned early last week, was arrested in connection to the murder probe, detained by police for intensive questioning and released without charge. Mr. Mizzi stepped down, as did economy minister Chris Cardona. The family of Ms. Caruana Galizia, including her son Matthew, an investigative journalist who covered the Panama Papers scandal, named Mr. Muscat, Mr. Schembri, Mr. Cardona and Mr. Mizzi as “complicit” in his mother’s death shortly after she was murdered.

Ms. Caruana Galizia was Malta’s best-known investigative journalist and spent years using her blog, Running Commentary, to make allegations of corruption that reached right into the Prime Minister’s office.

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She earned many enemies, was regularly denounced by One, the Maltese broadcaster that is owned by the Labour Party, and received flurries of libel notices, none of which broke her will to expose government corruption.

Her blog reported on the existence of secret Panamanian companies that Mr. Schembri and Mr. Mizzi had set up after the Labour Party won the 2013 election. Before her murder, she linked both men to secret payments made by Mr. Fenech through a Dubai company called 17 Black.

Last year, a Reuters investigation revealed Mr. Fenech was the owner of 17 Black, which was named in e-mails uncovered by Malta’s financial regulators as the vehicle to fund the secret Panamanian companies. Mr. Fenech was also a key player in Electro Gas, the consortium that won the bid in 2013 to build a gas-fired energy plant in Malta. Ms. Caruana Galizia questioned the legitimacy of the contract.

He family is calling for thorough investigations into Mr. Schembri, Mr. Mizzi and Mr. Cardona. All of them have denied any criminal activity related to the murder.

“I reiterate my deepest regret that a person who, with all her positive and negative qualities and contribution towards the democracy of our country, was killed in such a brutal way,” Mr. Muscat said.

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