The leader of the opposition, Adrian Delia, warned of “the collapse of democracy and freedom of expression,” and said on Twitter: “We shall not be silenced.”
Another opposition lawmaker, Simon Busuttil, warned on Twitter: “The rule of law has collapsed. Our democracy is at stake.”
Numerous officials condemned the killing. “If journalists are silenced, our freedom is lost,” said Frans Timmermans, the first vice president of the European Commission, the executive arm of the European Union.
Antonio Tajani, the president of the European Parliament, said that Ms. Caruana Galizia had “sacrificed her life to seek out the truth.”
Ms. Caruana Galizia started her journalism career in 1987 as a columnist for The Sunday Times of Malta, but she was best known in recent years for her influential blog, called Running Commentary, which frequently leveled accusations against powerful politicians and business executives. Her final blog post called the prime minister’s chief of staff “a crook” and warned: “There are crooks everywhere you look now. The situation is desperate.”
The European edition of Politico, the online news site, recently included Ms. Caruana Galizia on a list of 28 people who are “shaping, shaking and stirring Europe.” The news site called her a “blogging fury” and a “one-woman WikiLeaks” bent on exposing corruption and nepotism.
In February, Ms. Caruana Galizia wrote that the country’s economy minister and an ally had sued her for libel, and gotten her accounts frozen, after she accused them of visiting a brothel in Germany while on official government business.
The Times of Malta reported that Ms. Caruana Galizia had filed a police report about two weeks ago about threats that she had received.
Prime Minister Muscat called on the country to defend democracy and the rule of law.
“In this moment of profound sentiment, I am appealing for national unity,” he said in his statement. “This is not the time to discuss the conduct of a person. Everyone has the right to write and say what they want in this country, and those who feel wronged are entitled to protection by the courts and no other remedy.”
He vowed: “I will not rest until justice is delivered in this case, as our country deserves justice.”
Gerard Ryle, the director of the International Consortium of Investigative Journalists, which organized the Panama Papers investigation, said it was “deeply concerned about freedom of the press in Malta” and urged the authorities to investigate the killing. One of the victim’s three sons, Matthew Caruana Galizia, works for the organization as a developer and data journalist.
Ms. Caruana Galizia, who is also survived by her husband, had been a staunch advocate for the European Union, which Malta joined in 2004. “Over my dead body will my children be stuck on these rocks,” she told Politico.