Updated at 4:04pm with more reactions

The Caruana Galizia family on Wednesday welcomed the arrest of Yorgen Fenech, describing it as “an overdue and important development in the investigation” into the assassination.

In a statement, the family said it now expects the authorities to continue investigating the links that Daphne Caruana Galizia had uncovered between Mr Fenech and the prime minister’s chief of staff Keith Schembri and minister Konrad Mizzi.”

Earlier, activists and politicians insisted Prime Minister Joseph Muscat's position was no longer tenable and he should resign following the arrest of 17 Black owner Yorgen Fenech on Wednesday

Civil society calls for resignations

"Joseph Muscat should have fired Chief of Staff Keith Schembri and Tourism Minister Konrad Mizzi on the spot in February 2016. He didn’t. He protected them instead and still is, even after Keith Schembri withdrew his court case this week.

In doing so Joseph Muscat created the state of impunity – the Mafia State – that not only allowed a corrupt contract to be awarded, but led to the assassination of journalist Daphne Caruana Galizia," Repubblika, #occupyjustice and manueldelia.com said in a joint statement. 

Dr Muscat is accountable for what he described as “an assault on our democracy”, they said. 

"Now he must leave. If he doesn’t he must be fired. His party, his parliamentary group, Parliament have the power and the duty to have him removed if he does not go of his own free will," they said. 

Moviment Graffitti too said it was high time for both Mr Schembri and Dr Mizzi to "resign and disappear from the political scene".

"The arrest of Yorgen Fenech in connection with Daphne Caruana Galizia’s murder further makes the position of these two political figures totally untenable," the activists said.    

Should the pair not step down, "public anger would be entirely justified", the added, questioning Dr Muscat's continued refusal to remove them.

Family members react

One of Daphne Caruana Galizia's three sons, Andrew, reacted to the arrest by calling on Dr Muscat to hand over the "keys of justice" to someone else. 

Ms Caruana Galizia's sister, Corinne Vella, questioned why Dr Muscat had not yet "sacked" his chief of staff and Dr Mizzi despite both men "setting up Panama companies to receive kickbacks from Fenech's secret company 17 Black".

Arrest has 'clear political implications' - Adrian Delia

Speaking from a political congress in Zagreb, Croatia, opposition leader Adrian Delia said the entire country was passing through a delicate time.

He also made a distinction between the investigation and judicial process, and political responsibility that needed to be shouldered for this case.

“What happened in the past hours has clear implications and connotations.  I will hold back from commenting on the judicial process, justice must take its natural course… But I have a Constitutional duty to comment on the political implications of these developments,” he said.  

Dr Delia said Prime Minister Joseph Muscat had long been ignoring calls for the removal of his chief of staff Keith Schembri and Tourism Minister Konrad Mizzi.  

He said it was unacceptable that right now Mr Schembri was sharing an office with Dr Muscat and Dr Mizzi still held public office.

Muscat's position untenable - Simon Busuttil

Former Opposition leader Simon Busuttil was also quick to demand Dr Muscat steps down. 

"The Prime Minister's position is untenable. He must resign now and let justice take its course," Dr Busuttil said in a post on Twitter. 

In a statement, Partit Demokratiku said Mr Fenech is "intimately linked with the power establishment". 

"The police must be free from any influence, and the US Embassy's offer of help accepted. This is why all figures in government and Opposition who sought favours from Mr Fenech must leave now, starting with Keith Schembri and Konrad Mizzi. If Dr Muscat carries on protecting these people, then we know on whose side he's on," the PD said.

Similarly, Alternattiva Demokratika chair Carmel Cacopardo said that in light of the recent developments involving Mr Fenech, Mr Schembri and Dr Mizzi should be the first to resign or be removed. 

"After them, there are others. But step by step," he said.

Meanwhile, PN MEP David Casa said Dr Muscat's resignation now is "imperative". A number of other PN MPs have also called for Dr Muscat to step down.