Belgium has returned the remains of Congolese Prime Minister Patrice Lumumba, who was assassinated in 1961, to the Democratic Republic of the Congo.

A box containing one of Lumumba's teeth was presented to relatives at a ceremony in Brussels on Monday.

Prime Minister Alexander De Croo apologized to the family and spoke of his country's "moral responsibility".

De Croo stressed that to date there is "no evidence" of any active involvement by the Belgian government or the army in the assassination of Lumumba in the early 1960s.

Those responsible in Belgium could probably have prevented the crime.

In addition to Lumumba's children, Congolese Prime Minister Jean-Michel Sama Lukonde also attended the ceremony.

During a visit to the Democratic Republic of the Congo almost two weeks ago, King Philippe of Belgium expressed his "deep regret" at the suffering of the colonial era.

He now received the relatives of Lumumba in his palace.

Lumumba was the first democratically elected head of government of the long-standing Belgian colony of the Congo.

The declared opponent of the colonial rulers was murdered by a killing squad a few months after his election; his body was never found.

Research many years later revealed that his body had been dissolved in acid - only the tooth remained as it had been removed earlier.

Belgian authorities found the tooth decades later while investigating Lumumba's disappearance.

He is now to be transferred to his home country.

The case strained relations between Brussels and Kinshasa to the end.

Patrice Lumumba remains an important figure in African history to this day because of his struggle for independence and liberation from colonization.