The assassins who killed Panama Papers journalist Daphne Caruana Galizia used a fatal text message sent from a boat out at sea, according to a report.

Authorities on the Mediterranean island of Malta arrested ten people for the explosion last month that killed the lauded 53-year-old blogger known for her criticism of the government.

Three have now been charged, with a report in Malta Today on Wednesday revealing details of the investigation, including how they allegedly set off the powerful bomb on her car.

Brothers George and Alfred Degiorgio, 54 and 52, were joined by Vincent Muscat, 55, in the reported scheme, which involved an electronic device attached the explosive that was put on the vehicle the morning of the blast.

Ten arrested in assassination of Panama Papers journalist

A bomb killed Daphne Caruana Galizia and destroyed her car on a rural Malta road. (STR/AFP/Getty Images)

George Digeorgio, stationed on a boat out at sea, is alleged to have sent the text message to the device that triggered the killing after receiving a signal from his brother, Malta Today reported.

Seven other men, all of them Maltese, were released on bail as authorities continue the investigation into those already charged, who all have previous criminal records.

Galizia's family has repeatedly questioned the independence of the investigation by authorities, who were often the target of her blog.

Maltese investigative journalist Daphne Caruana Galizia was known for her criticism of the government. (DARRIN ZAMMIT LUPI/REUTERS)

The slain journalist was most famous for using information in the Panama Papers leaks to allege illicit activity between the inner circle of Maltese Prime Minister Joseph Muscat and the ruling family of Azerbaijan.

Russian independent journalist stabbed in neck at Moscow office

Reports after her death said the explosive Semtex was used in the bomb, prompting speculation that the weapon came from somewhere other than the island off the coast of Sicily.

Sources close to the investigation told multiple news outlets on Wednesday that the explosive was instead TNT.

Prosecutors have not released a motive for the killing.

Sign up for BREAKING NEWS Emails privacy policy Thanks for subscribing!