VALLETTA (Reuters) - Yorgen Fenech, a prominent businessman arrested on Wednesday in connection with investigations into the murder of Maltese journalist Daphne Caruana Galizia, was released on bail on Thursday evening, police sources said.

He will be under round-the-clock police surveillance as investigations continue.

Caruana Galizia, renowned for her work in exposing corruption, was killed by a car bomb near the Maltese capital Valletta in October 2017 - a murder that shocked Europe and raised questions about the rule of law on the small island.

Eight months before her death, she wrote about a mysterious company in Dubai called 17 Black Limited, reporting that it was connected to Maltese politicians but offered no evidence.

A Reuters investigation last year revealed that Fenech was the owner of the firm.

He was arrested on board a yacht shortly after it left Portomaso marina early on Wednesday morning.

A day earlier, Prime Minister Joseph Muscat offered to pardon a suspected middleman in the murder if he provided legally binding evidence of who was behind the killing.

Muscat said on Thursday that so far the suspected middleman had not given complete information.

Under Maltese law, the police had until early Friday morning to either charge or release Fenech.

Around 2,000 protesters took to the streets of central Valletta on Wednesday evening to denounce Muscat’s government. At one point they blocked Justice Minister Owen Bonnici in his car and chanted “Justice”, “Mafia” and “Shame on you”.

Three men suspected of being Caruana Galizia’s killers were arrested in December 2017, but police have struggled to determine who commissioned the murder.