Back in 2006 Paul Kagame and other top Rwandan officials were indicted by a French judge for the shooting down of the former president's plane in 1994. This was a major trigger of the Rwandan genocide, but there is little evidence and many suspects in the case. The Rwandans responded by kicking all French organisations out of the country.
Under EU cooperation agreements, EU member countries are required to carry out arrest warrants of other member states. This, Germany did for one Rwandan official, Ms Kabuye, Chief of Protocol for the President, traveling through the country. This afternoon there were spontaneous government-ordered protests in the centre of Kigali and in front of the German embassy. (UPDATE 12/11: And the German embassador was asked to leave.)
On the arrest, the BBC writes:
Ms Kabuye has visited the country before but under German law could not be arrested as she was part of an official delegation. "Rwanda has been made aware on several recent occasions that if Ms Kabuye returned to Germany she would be arrested," said [a German] diplomat.
Al Jazeera quotes the Rwandan Information Minister who confirms :
Louise Mushikiwabo, Rwanda's information minister, said that Kabuye was not surprised at being arrested on arrival in Frankfurt.
And in the Rwandan pro-government New Times:
[Foreign affairs minister Rosemary Museminali] said that prior to her travel, the German government had warned Kabuye that she risked being arrested...Seems clear. But then the Rwandan New Times quotes the Foreign Affairs Minister:
“We emphasised in the note that Kabuye ... was performing diplomatic duties and therefore the Germany authorities wouldn’t have arrested her...” said [Foreign Affairs Minister Museminali.
And to finish, who can explain how the whole "indictment -> arrest -> trial -> verdict" thing works?
"We have always been surprised that people can take these bogus indictments seriously. How can you condemn someone before even bothering to hear their side of the story?” [Justice Minister Tharcisse Karugarama] wondered. (New Times)