A prominent Maltese businessman has been arrested onboard his yacht as it was heading out to sea, in an operation linked to the murder of the Maltese anti-corruption journalist Daphne Caruana Galizia.

Armed forces personnel boarded a vessel at about 5.30am on Wednesday and detained Yorgen Fenech.

The arrest came less than 24 hours after Malta’s prime minister offered immunity from prosecution to an alleged middleman in exchange for information about those who ordered the murder of the journalist two years ago.

One of the last investigations on which Caruana Galizia was working at the time of her death was a massive leak of data from Fenech’s business.

Police did not officially comment on the operation, but a high-ranking police source told AFP: “We have arrested a man as part of our investigations into the murder of Daphne Caruana Galizia.” Fenech was “a person of interest” in the case, the source added.

Officers have 48 hours in which to bring charges against Fenech.

Police onboard Yorgen Fenech’s yacht Gio, after it was intercepted by the Maltese military early on Wednesday and forced back to Portomaso, Malta. Photograph: Jonathan Borg/AP

Addressing journalists shortly after the arrest, the Maltese prime minister, Joseph Muscat, confirmed Fenech’s detention and described him as a “person of interest” in the case. He said there was nothing pointing towards the involvement of members of his administration in the murder.

It emerged on Wednesday that control of Fenech’s Tumas Group businesses, which span energy, property and gaming, were passed to family members on 12 November.

Galizia, whose work exposed corruption among Malta’s political and business elite, was killed by a car bomb in October 2017. Within a few weeks three men accused of planting the explosive device were arrested and are awaiting trial, but those who masterminded the murder are yet to be identified.

Concerns about the time it has taken to bring her killers to book have led to questions about the rule of law in Europe’s smallest member state. Malta’s opposition leader responded with fresh calls for the prime minister’s resignation.

A subsequent investigation by the Daphne Project, a collective of journalists set up to continue Caruana Galizia’s reporting and investigate her death, reported last year that Fenech was the owner of a shell company called 17 Black.

A mass in Valletta in April 2018 in memory of the murdered journalist Daphne Caruana Galizia. Photograph: Matthew Mirabelli/AFP via Getty Images

Caruana Galizia had reported that 17 Black was due to make substantial payments into two other shell companies, registered in Panama, and belonging to two members of the country’s ruling Labour administration. The information had come from the Panama Papers, a leak from a firm of offshore lawyers.

Fenech’s consortium secured a government concession to create a power station at Delimara, which produces one of the island’s two main supplies of electricity. Emails from the power station company, Electrogas Malta, were being leaked to Caruana Galizia at the time of her death.

A subsequent investigation by Malta’s financial intelligence unit uncovered an email that suggested that a company belonging to the then energy minister, Konrad Mizzi, and the prime minister’s chief of staff, Keith Schembri, were due to receive up to $2m in payments within a year from 17 Black.

The German engineering group Siemens, which co-owns Electrogas Malta with Fenech, told reporters for the Daphne Project on Wednesday that Fenech had resigned as a director. It added that it was not aware of any indications of misconduct on the part of Siemens or its employees.

Schembri and Mizzi both told Reuters in October 2018 they had no knowledge of any connection between 17 Black and Fenech, or of any plan to receive payments connected to Fenech or the energy project.

In a statement to Reuters, Schembri said he had not heard that Fenech owned 17 Black. He said he was not involved in the power station project and, asked by Reuters if he had intended to profit from the project, said: “The answer is a categorical ‘No’.”

Mizzi, who is now tourism minister, issued a statement through a spokesman in October 2018 saying he “reiterates that there is no connection, direct or otherwise, between him, the company or trust he held, and any entity called 17 Black. Furthermore, he has no information relating to 17 Black.”

Fenech said last year that he and his companies “never had (or intended to have) any untoward business relation” with any politicians or politically affiliated individuals or entities.

His lawyer could not immediately be reached for comment on Wednesday.

Witnesses quoted by the Times of Malta said Fenech’s motor yacht was intercepted by an armed patrol boat as it left the Portomaso, north of the capital, Valletta.

In a statement, Caruana Galizia’s family welcomed the arrest, saying it was “overdue”. They added: “We now expect the authorities to continue investigating the links our mother uncovered between Fenech and the prime minister’s chief of staff and minister Konrad Mizzi.”

Pressure is building on Mizzi and Schembri to step down.

The MEP Sven Giegold, who helped produce a parliamentary report into Caruana Galizia’s death, welcomed the progress after what he described as “two years of inaction”.

He said: “Given the links between the suspect Yorgen Fenech, his company 17 Black and the minister for tourism, Konrad Mizzi, and the chief of staff, Keith Schembri, both must now step down.”