Queen Rosalie Gicanda (L) was revered by many Tutsis
One of the most wanted suspects in Rwanda's 1994 genocide has been arrested in Uganda.
Idelphonse Nizeyimana was an intelligence chief at the time of the genocide, in which about 800,000 Tutsis and moderate Hutus were killed.
He has been extradited to Tanzania for trial at a UN-backed tribunal, accused of organising the killing of thousands - including the former Tutsi queen.
Rwanda welcomed the arrest but said he should be tried in his country.
"There is no time limit for justice, whether it comes fast or slow it is something we want to see," said Augustine Nkusi, a spokesman for the prosecutor-general.
"Fifteen years is very little compared to what was committed in Rwanda. There are many victims who have not yet forgotten, who have not yet received justice."
Mr Nizeyimana, an army captain, was head of intelligence and military operations at Rwanda's elite military training school, the ESO, during the genocide.
The lengthy indictment says he elaborated, adhered to and executed a plan to wipe out the Tutsis - the minority in a country ruled by a Hutu government for more than three decades.
He is accused of setting up special military units to help carry out the slaughter.
One of these units is believed to have killed Queen Rosalie Gicanda, widow of King Mutara III who died in 1959 shortly before the country became a republic.
Rwandan justice minister Tharcisse Karugarama: " I think that justice has arrested this guy"
According to a 1999 report by US-based Human Rights Watch, Hutu soldiers took the queen from her home in the south-eastern town of Butare and shot her behind the national museum.
They also murdered several women who looked after the queen, who was about 80 years old when she died.
Another charge against Mr Nizeyimana is that he ordered the establishment of roadblocks at which Tutsis were captured before being murdered.
And troops said to have been under his command rampaged through the University of Butare, killing lecturers and students in what was seen as an attempt to wipe out the Tutsi intelligentsia.
Like an estimated two million Rwandan Hutus, Mr Nizeyimana fled after the genocide and took refuge in neighbouring DR Congo.
Idelphonse Nizeyimana allegedly helped draw up death lists
Officials believe that there he was active in a pro-Hutu rebel army called Democratic Front for the Liberation of Rwanda (FDLR).
The BBC's Geoffrey Mutogoma in Kigali says it is believed he rose to the rank of colonel in the FDLR and Rwandan officials hope his arrest will disrupt its activities.
He was arrested in a modest hotel in the Ugandan capital, Kampala.
Ugandan police said he had crossed the border from DR Congo last week, and was heading for Kenya with false travel documents.
The International Criminal Tribunal for Rwanda, based in Arusha, Tanzania, said he would appear before the judges in the coming days.
The tribunal, which is due to finish its work by the end of next year, says it is still trying to find 11 fugitives. So far 40 people have been convicted of crimes connected with the genocide.