A Gambian former interior minister is set to go on trial in Switzerland, charged with crimes against humanity.

Ousman Sonko fled there in 2016, shortly before Gambian President Yahya Jammeh, accused of heading a repressive regime, lost power.

Mr Sonko was arrested after non-governmental organisations presented evidence of his alleged involvement in human rights violations.

But his lawyer said that he was not responsible for what happened.

Philippe Currat is quoted by the AFP news agency as saying that The Gambia's National Intelligence Agency, which was "never... under [his] authority" was behind the alleged crimes.

Switzerland is trying the case under the principle of universal jurisdiction, which allows countries to prosecute people on their territory, even though the alleged crimes have been committed elsewhere.

Human rights groups believe the case could be a warning to repressive governments everywhere that the arm of the law can be very long indeed.

Switzerland's charge sheet against Mr Sonko is extensive.

It includes the participation in, or ordering of, killings, torture, and rape - all targeting political opponents. These could all constitute crimes against humanity under Swiss law.

Swiss investigators travelled to The Gambia and interviewed dozens of alleged victims and witnesses - nine will be in court to testify.

Mr Sonko is the highest-ranking government official ever to be prosecuted under universal jurisdiction in Europe.

From 1996 until 2016, The Gambia was ruled by President Yahya Jammeh, whose time in office, according to Human Rights Watch, was characterised by "widespread abuses, including forced disappearances, and extrajudicial killings".

Mr Sonko was Mr Jammeh's right-hand man, his role as interior minister putting him in charge of the security services, including, allegedly, a sinister paramilitary group known as "the Junglers".

But in 2016, shortly before Mr Jammeh himself lost power, Mr Sonko fled to Switzerland, where he claimed asylum.

Within months he was arrested, after an NGO, Trial International, gave the Swiss authorities details of abuses he was allegedly involved in.

After six trips to The Gambia and 40 interviews with complainants, the Swiss attorney general drew up the charge sheet

Benoit Meystre of Trial International views the application of universal jurisdiction as "a key legal principle that sends a signal to other [alleged] perpetrators... that [they] cannot remain unpunished - or at least unprosecuted".

The case against Mr Sonko is being seen as particularly significant.

Although a number of European countries have begun using universal jurisdiction, he is the highest-ranking former government official ever to be tried in this way.

It is also only the second time Switzerland has ever tried someone under universal jurisdiction for crimes against humanity.

The first case, in June 2023, saw former Liberian militia leader Alieu Kosiah sentenced to 20 years for crimes including rape, murder, and cannibalism.

Other countries are also bringing cases against former members of Mr Jammeh's regime.

In October, Germany handed a life sentence for crimes against humanity to Bai Lowe, a one-time member of "the Junglers".

Later this year, a court in the US state of Colorado will begin the trial of an alleged former member of the same group.

Although The Gambia has created its own transitional justice process to address abuses committed under Mr Jammeh's rule, human rights groups say its work has so far been very slow.

Even in the Swiss trial against Mr Sonko, one of the plaintiffs who had been scheduled to testify died before the case came to court.

But for those who do testify, "being invited before a court of law, to tell their stories, is a way for them to heal. And if the federal court does reach a guilty verdict, it will be an enormous relief for them. They will get the answers they have been waiting for for many years," Trial International's Mr Meystre said.