Rule-of-law NGO Repubblika on Friday accused former minister Joseph Muscat of "vile intimidation" of a court expert.

The criticism comes a day after a criminal complaint was filed against court expert Miroslava Milenovic, by lawyers representing Muscat and other defendants charged in connection with the Vitals hospital concession.

Milenovic was appointed as one of the forensic accountants by Magistrate Gabriella Vella when conducting the inquiry into the now-annulled hospitals privatisation deal.

The expert was summoned as a witness on Wednesday when proceedings continued against Muscat and the other co-defendants. Under tight cross-examination by Muscat’s lawyers, she said that she never obtained a warrant as an accountant but insisted that she was a “qualified accountant.”

Repubblika said on Friday it will not tolerate intimidation and threats towards investigators, prosecutors and magistrates and the activists will not remain silent when faced with a "mafia organisation that uses threats and intimidation to flee justice".

"This vile intimidation is taking place as the expert found proof that spells trouble for Muscat and his friends.

"He couldn't discredit the proof, and therefore, he trying his best to discredit and intimidate the person who collected the proof."

The same expert was identified as a forensic accountant in the Egrant inquiry, however, Muscat had not discredited her then, Repubblica added.

"Muscat threatens whoever he thinks is an obstacle between the crime he committed and the impunity he expects to benefit from."

The NGO also referred to comments by PL's Jason Micallef, who on Thursday said Muscat will return as PN's and Repubblika's "nightmare".

Micallef was recently appointed as the PL's "special delegate on the implementation of the electoral manifesto' and he will report directly to the party's central administration. 

Repubblika said Micallef was trying to intimidate state officials who were willing to fulfil their roles as required by law.