An NGO boss who was among four suspects held in pre-trial detention as part of a Belgian probe into alleged bribery in the European Parliament linked to Morocco and Qatar has been released.

Niccolo Figa-Talamanca, an Italian who led the "No Peace Without Justice" NGO before being stripped of his position after his arrest in December, was ordered freed on Friday, prosecutors said.

The newspaper L'Echo reported that Mr Figa-Talamanca's release was granted after police questioned another NGO chief, former Italian MEP Pier Antonio Panzeri, who has cut a plea deal in exchange for providing evidence about the alleged bribery.

A spokesperson for the federal prosecutor's office refused to comment on a link between the reported testimony by Mr Panzeri and Mr Figa-Talamanca's release.

"At this stage, the evidence in the case no longer justifies his detention," the spokesperson said.

The two NGOs run by Mr Panzeri and Mr Figa-Talamanca shared the same Brussels address.

Niccolo Figa-Talamanca (image credit: No Peace Without Justice)

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Prosecutors suspect money was funnelled via at least one NGO to influence parliamentary decisions in favour of Qatar and Morocco. Police raids in December on homes of MEPs, parliamentary aides and lobbyists turned up €1.5m in cash.

The others who remain in custody are Mr Panzeri; Greek MEP Eva Kaili, who was one of the parliament's 14 vice presidents before being stripped of that position; and Ms Kaili's Italian boyfriend Francesco Giorgi, who was a parliamentary aide.

Belgian law enforcement quietly started their probe into the alleged graft in mid-2022, putting Mr Panzeri and others under surveillance.

Qatar and Morocco deny any wrongdoing in the case.

Ms Kaili asserts she is innocent while Mr Giorgi has reportedly partly confessed. The four arrested in December were charged with bribery, money-laundering and being involved in a criminal organisation.

Mr Panzeri is reportedly said to have minimised the involvement of Mr Figa-Talamanca in the case.

The corruption probe has shaken the European Parliament and cast a shadow over other EU institutions in Brussels.

Last week, the parliament lifted the immunity of two other MEPs, Belgian lawmaker Marc Tarabella and Italian legislator Andrea Cozzolino, at the request of Belgian authorities.

That step opens the way for them to be questioned in the probe, should investigators choose. Both MEPs deny any wrongdoing.