Why did Louis Riel send Ambroise Lépine to kill thomas Scott?

Answer 1

Louis Riel was head of the Red River Government put into place after the residents were "sold" to Canada in a land deal with the HBC.

Thomas Scott, a Canadian, believed that the Red River residents and their land were included in the purchase and as such should be ruled by Canada.

Thomas threatened to assassinate the Red River leader which resulted in him being arrested and tried for treason.

Even then he may have avoided the death sentence, as other Canadians did, but while being held he was openly contemptuous and insulting which lead to Ambroise overseeing a trial at which Scott received the death sentence.

Scott was executed by firing squad.

That is more what than why. Why is debatable but it seems clear to many that the Red River residents were well within their rights to have a representative government of their own choosing. They themselves nor their land could not have been included in the sale by HBC and as such were not part of that deal.

Canada of course choose to believe they purchased everything including people and that they were the rightful rulers and any governments would be answerable to them and not the residents or people.

Riel was almost certainly trying to show Canada and the world that they were the legitimate government and as such were exercising rights that every such government at the time had.

Canada would use the sharp end of a bayonet and promises of rights in the Manitoba act to create a Canadian province and Canadian rule. That resulted in more pointy bayonets, fewer rights and yet another rebellion.