The investigation into the murder of Daphne Caruana Galizia risked being totally derailed as Melvin Theuma, the middleman-turned-state-witness in the case, was caught moving key evidence from his house at the time of his arrest, according to sources close to the investigation.

“Melvin was basically caught red-handed trying to move the evidence that he had been keeping at his home in the outskirts of Żurrieq. When he was arrested, he claimed to be on his way to hand himself and the evidence in, but we do not believe that was the truth,” the sources said.

Instead, the likeliness is that Mr Theuma, who admitted in court, under cross-examination by lawyer Jason Azzopardi, to having had advanced knowledge of his arrest, was preparing to move evidence in the case.

The evidence included a plastic box containing mobile phones, two bundles of papers, a SIM card and a USB pen drive with damning recorded conversations concerning the murder between himself and Yorgen Fenech – the man he identified as the mastermind in the case.

The box also contained a photo taken inside the Auderge de Castille of himself with Keith Schembri, the former chief of staff of the prime minister. At this stage, it is still unclear why he planned to shift or destroy the evidence he himself had compiled.

Mr Theuma, 41, was last month granted a presidential pardon in exchange for testifying and providing corroborative evidence in the murder case.

There would have been no breakthrough in the case

The operation for his arrest was meant to take place on November 16, leaving enough time for warrants to be issued and for the inquiring magistrate to be briefed.

In court, lead investigator Keith Arnaud said a meeting was held the weekend before the arrests at the Malta Security Services offices for which Europol officers were present. During that meeting, it was agreed to move in on Mr Theuma on the following Saturday.

However, the Thursday before that, the security services team who had been monitoring Mr Theuma throughout the investigation flagged that he had suspiciously broken off from his normal routine and was about to move the plastic box. Investigators knew about the existence of the box and the evidence inside, as well as its approximate location inside the house prior to the arrest.

In fact, while the plan was to arrest Mr Theuma on money laundering charges based on investigations carried out on his illegal lotto business, the target was to retrieve the plastic box and then leverage the evidence to produce a confession that leads to the person or people who commissioned Ms Caruana Galizia’s assassination.

“The evidence he was moving was central to the case and had it been lost, the case would have likely hit a brick wall… we were literally hours away from losing everything,” the source said.

A decision was taken to move in and arrest Theuma on the spot by Inspector Nicholas Vella, who was the Economic Crimes Unit officer assigned to this part of the investigation, and MSS agents form a team dedicated to the Caruana Galizia murder probe.

Mr Theuma was arrested in Żurrieq, while his partner and her daughter were arrested in an apartment in Marsascala believed to have been the operations centre for his illegal gambling operation.

“We believe that had it not been for this decision, taken in the moment, without it filtering through the entire chain of people informed about this operation, the evidence would have been moved and there would have been no breakthrough in the case.

“There were several instances throughout the past two years where we realised there was sabotage but we could not establish where it was coming from. This was one such instance.”

Mr Theuma has been central to the dramatic court testimony surrounding the 2017 car bomb murder. He told the court how he arranged payments to the three men alleged to have carried out the murder of the 53-year-old journalist.

In his testimony, the Birkirkara taxi-driver said he hadn’t been paid “a single cent” for his own part as the middleman and that his former “friend”, multi-millionaire Tumas Group magnate Fenech, was the “only mastermind”.

He also described meetings with various members of Prime Minister Joseph Muscat’s staff, including his chief aide Keith Schembri, and the way it was arranged for him to get a government job despite never applying for it.