Physicist Adlène Hicheur had no idea that his life was about to be turned upside down when he joined a video conference from his home in Rio de Janeiro, Brazil, this summer to discuss his paper ‘Studies of Bc + Meson decays to three-body final states at LHCb’ with collaborators at CERN and elsewhere.

Police waiting downstairs whisked him to the airport, where he was summarily deported the same day. Since then, Hicheur has since found himself in a disturbing situation, detailed in a News story.

Brazilian authorities sent him to France, where Hicheur has a 2012 conviction for terrorism-related offences (and served a short prison sentence). The French authorities placed him under house arrest, operating under sweeping detention powers given to them as part of the state of emergency declared after terrorist attacks in the country.

Leaving aside the fact that Hicheur’s conviction has been vigorously contested by many scientific colleagues, a fundamental legal principle in a democracy is ‘double jeopardy’, which says that someone cannot be tried twice for the same offence. Yet this is effectively happening to Hicheur, both in Brazil and France. Likewise, another principle is that those who have served their sentence should have the right to pursue a new life unhindered — yet Hicheur, who by all accounts was successfully making a fresh start after moving to Brazil in 2013, and contributing productively to the country’s science, has been denied this chance.

Whether one agrees or disagrees with Hicheur’s house arrest — and many of his colleagues have denounced it as brutal, unjustified and unnecessary — at least it has a semblance of legal logic under the exceptional temporary situation in France.

The haste and circumstances of the action seem to violate Brazilian law.

That cannot be said of Hicheur’s ejection from Brazil, which in the absence so far of a valid explanation seems to smack of arbitrariness linked to pre-Olympics tension and recent widespread coverage by Brazilian media of his past conviction. Moreover, the haste and circumstances of the action seem to violate Brazilian law, human rights and international treaties to which Brazil is a signatory.

The incident is all the more perplexing because Brazil’s justice minister acknowledges that Hicheur was a law-abiding citizen during his time in the country, and France has not raised any new allegations against him. It is also difficult to reconcile the physicist described by his colleagues with the account of Hicheur in the French interior ministry’s house-arrest order, which says there are “serious reasons” to think that he constitutes a security threat.

The reaction of Ignacio Bediaga, head of the group at the Brazilian Center for Physics Research in Rio de Janeiro where Hicheur first worked when he came to Brazil, echoes that of many of the deported physicist’s colleagues: “Hicheur performed an exceptional job, showed exemplary moral and ethical behaviour and a great willingness to collaborate with the group.” He adds that at no time did anyone in the group perceive anything amiss with Hicheur’s conduct.

Science allowed Hicheur, a Franco-Algerian citizen born in Algeria, to reach the heights of working on the Large Hadron Collider ‘Beauty’ experiment, better known as LHCb. After he became a persona non grata in European research organizations following his conviction, his international colleagues helped to find him a place to start afresh in Brazil and continue his science.

Hicheur deserves a fair and full hearing. The best route could be the Brazilian courts, and colleagues and academics there deserve support alongside Hicheur’s lawyers for their efforts to pursue the case. Were Hicheur’s deportation revoked, this might open the way for his return to work in Brazil, and thus make it easier for France to lift his house arrest.

In France, Hicheur is appealing his detention. But in the current climate of fear, the judicial machinery may be harder to mobilize.

French President François Hollande and his government, in their engineering of the state-of-emergency laws, have to their credit sought a difficult balance between giving police extra powers to help them fight the terrorist threat and preserving fundamental liberties and civil rights. But there is nonetheless the risk that such measures will be misused.

And if an intelligent and articulate individual such as Hicheur (a Muslim) with a bevy of support from his scientific colleagues can find himself helpless, what then of the many others with much less capacity to defend themselves? Fairness, freedom, the rule of law and human rights — including the right to a defence ­— are the basis for a democracy. It is not easy in these times to defend these values, much less for someone convicted in the past of terrorism-related offences, but defend them we must.