Daphne Caruana Galizia was killed in October when the vehicle she was driving exploded near her home, with loved ones blasting the government that she needled with her blog. The European Commission has called on Malta to get to the bottom of the crime.
All of the suspects are from Malta and most have criminal records, NPR's Frank Langfitt reports, citing Maltese Prime Minister Joseph Muscat.
The 53-year-old was known for her blog accusing top politicians of corruption.
As NPR's Sylvia Poggioli reported in October, Caruana Galizia's independently operated website "often drew more readers than the total circulation of Malta's newspapers".
Eight people have been arrested in the death of the journalist assassinated in her native Malta after exposing alleged corruption through the Panama Papers.
Her criticism was also levelled at Prime Minister Joseph Muscat and his aides, who she accused of being linked to offshore companies and payments from the government of Azerbaijan.
Overall, Mr Muscat gave nearly no details, citing concerns any information could compromise prospects to prosecute the case.More news: Former Egyptian PM Ahmed Shafiq left Emirates to Cairo
Latching onto a retweet by the government's chief spokesman that several suspects could be charged with Daphne Caruana Galizia's murder, her son has lamented the lack of information given to the family. Farrugia said he wouldn't disclose anything else because 'I have been already threatened by legal action by the Caruana Galizia family'.
Caruana Galizia's family reacted angrily to how the arrests were announced on Monday, saying police should have informed them before the prime minister.
The journalist's family alleged last month that Farrugia had put the investigation at risk by sharing confidential information with lawmakers.
The investigation appeared to be continuing, as police and armed forces had cordoned off an area in Marsa, a small town close to Valletta, the capital.
The arrests were the first apparent break in the murder investigation, which is receiving support from the FBI, Europol, and Finnish security services.
Investigators have 48 hours to question the suspects to decide whether to seek charges, in accordance with Maltese law. "As soon as I learned about this barbaric act, I said that we will leave no stone unturned".