By Mark Doyle
BBC World Affairs correspondent
The pressure group Human Rights Watch (HRW) has welcomed the arrest of Hissene Habre, former president of Chad and the man it calls the "African Pinochet".
Hissene Habre's regime is accused of torture and political murder
Mr Habre took power in 1982 after a long military campaign and was in turn overthrown in a coup d'etat in 1990 by the current president of Chad, Idriss Deby.
He then went into exile in Dakar, the Senegalese capital.
Since then, HRW has been instrumental in helping Chadian victims of the former dictator shape a series of detailed allegations against his regime.
Mr Habre has now been arrested in Senegal on an international warrant issued by Belgium for crimes allegedly committed during his time in power.
HRW investigator Reed Brody has personally been pursuing Mr Habre for more than six years.
Standing outside the state prosecutor's office in Senegal, Mr Brody told the BBC by mobile phone: "This could be the first step in extraditing Habre to Belgium."
In Chad, a truth commission set up after Mr Habre's overthrow accused his regime of political murder and systematic torture.
And in Mr Habre's country of exile, Senegal, a court heard the details of 97 political killings, 100 "disappearances" and widespread torture, all aimed at Mr Habre's political or ethnic opponents.
But political pressure foiled the cases in Chad and Senegal.
Idriss Deby overthrew Hissene Habre in a coup d'etat in 1990
In Chad, the problem appeared to be that many members of Idriss Deby's team were also prominent under Mr Habre.
In Senegal, legal moves to prosecute Mr Habre for war crimes reached an advanced stage.
However, the investigating judge, Demba Kandji, was then removed from the case by a panel chaired by Senegal's President Abdoulaye Wade.
Subsequently, more alleged victims of the former Chadian leader, this time in Belgium, brought a new case.
A Belgian judge, Daniel Fransen, investigated their claims - and an international arrest warrant and an extradition request from the Belgian government followed.
If Mr Habre's arrest and questioning are the first steps in his extradition to Belgium, the former Chadian leader would be in the highly unusual situation of being a former head of state facing his alleged victims in the courts of another country.
Hissene Habre is widely believed to have come to power in Chad with covert support from the CIA.
Some reports say the US agency gave him $10m (£5.8m) for his campaign to take power.
The US saw him as a bulwark against Colonel Muammar Gaddafi in neighbouring Libya.
Chad has always had strategic significance; its proximity to Libya is just one important factor.
This piece of the Sahara Desert has also been important historically because it was territory sought by British and French colonialists as a crossroads linking other conquests.
In the days before fast planes and satellite communications, it was seen as hugely important in Paris and London to have linked colonies.
In the end the French got Chad, which linked up other French territories to the west and the south.
The British got neighbouring Sudan.
But Sudan only linked to British-controlled Kenya and other states to the east and not, as London would have also wished, to Nigeria to the west: French-controlled Chad got in the way of that.
Nostalgic old-colonial feelings had only just began to wane in Europe when, a decade ago, Chad discovered large quantities of oil - boosting the significance of the place once again.