The independent Congo Free state was created on July 1 1885. It's army/militarized police, the Force Publique, was officially created by a decree on October 30 1885 but a proto-force had already existed since 1879 when Leopold II commissioned several expeditions into the Congo basin.

It's important to realize that the Congo Free State was a very weird construction.

1. It's independence was declared by a private company owned by Leopold II without clear borders, Portugal managed to retain most of the coastal territories claimed by Leopold II, his claim on the southern disputed Katanga region was accepted by accident by Great Britain.
2. Leopold II got international approval for his sovereignty over Congo (with undefined borders) but his sovereignty wasn't officially accepted, an important legal distinction. The 14 major powers didn't want to create a permanent situation but rather used Leopold II as a temporary place holder for the region.
3. Leopold II was the King of Belgium and the Belgian government gave him the permission to become sovereign of the new Congo Free state but only in his personal name and not in his capacity as King of Belgium. The Belgian state itself had no interest in a colonial adventure. Leopold II had to pay for everything from his (massive) personal wealth.

Belgium did not support the King's colony financially but after 5 years Leopold II was nearly bankrupt so the Belgian state had to loan him 25.000.000 Golden franks to keep his colony running, in addition he started selling even more exploitation rights to certain parts of the Congo to private companies.

To enforce his rule over the Congo Leopold II started hiring African mercenaries and European officers.

Between 1883 and 1901 Leopold II would hire 12.452 mercenaries.

• 5.585 Haoussas
• 2.745 Sierra Leone
• 1.775 Zanzibar
• 708 Liberia
• 591 Gold Coast
• 412 Abyssinia
• 223 Egypt
• 215 Somalia
• 198 Dahomey

The officers were European, mainly Belgian but also included some Scandinavians and Italians. I've only got the numbers for the Scandinavians and Belgians.

Scandinavians hired between 1878 and 1914:

• Danes 53 officers 4 non-commissioned officers
• Norwegian 26 officers 3 non-commissioned officers
• Swedish 47 officers 18 non-commissioned officers

Belgian Officers in the Force Publique between 1878 and 1908

• 648 Officers 1612 non-commissioned officers

Of those 2260 Belgians 662 would die in the Congo.

The foreign mercenaries would be steadily replaced by natives. The first training camp was at Vivi where the first 10 Bangala arrived in September 1884 but training on a large scale only starts in august 1886 when Captain Roget together with 12 soldiers starts a training camp in Boma. In a small 2 years 2000 natives are trained and by 1901 nearly all African mercenaries are replaced by native soldiers. The officer corps remains completely European, non-Belgians would replaced when Belgium took over the colony from Leopold II in 1908.

So to answer your question:

Is it true that Belgian troops were not involved in the Congo Free State or any crimes committed there? Yes, no Belgian forces were even in the Congo but Belgians and other Europeans, mainly ex-military, were in command of the expeditions and the military campaigns.

Or the crimes were committed by native Congolese themselves? In the early phase when Leopold II was establishing his rule his army was mostly foreign mercenaries. The very exploitative rubber harvesting started from 1895 onward and at that time the Force Publique was steadily changing into a purely native trained armed police force with European officers. A small caveat has to added though that the term Congolese at that time was a very broad collection of perhaps nearly 250 different ethnics/languages/tribes. Soldiers drafted from one region were often deployed in other regions.

Commanded by European officers of many different nationalities? Yes, every order was nearly always European, non-commisioned native officers existed but this was the highest rank they could achieve.

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Congo tentoongesteld. Een geschiedenis van de Belgische antropologie en het museum van Tervuren (1882-1925), Acco, Leuven, 2005

Léopold II et la Force Publique du Congo. Leopold II en de Openbare Weermacht van Congo 1885-1985. Tentoonstellingscatalogus, Brussel, 1985

Gann, L.H. en Duignan, Peter, The Rulers of Belgian Africa 1884-1914, New Jersey, 1979, p. 225.