I don’t understand how you can be convicted of murder in Denver for something that happened in Zambia. Why wasn’t he extradited to Zambia and tried there? I don’t doubt that he’s guilty, but the US doesn’t have jurisdiction in Zambia unless there’s something that I missed.
Some decades ago, thus I can't quote the law verbatim. In Brief:
An American can without consequence under U.S. law plan to kill any other nationality any where in the world. They can be prosecuted if applicable under that nation's law(s).
Should that person or persons execute such plan on U.S. soil, to include any territory can be punished for murder and other crimes under U.S. laws.
Should the person or persons execute such a plan they can be extradited, if applicable, to such country for prosecution for crimes.
Should an American plan or violate any crime associated with the killing of another American regardless where the murder or plan to murder were to be committed on U.S. soil or territory or other country the person or persons are prosecutable by a [Federal] U.S. court on U.S. soil or territory.
Basically, hypothetically, with stipulations according to international agreements between the U.S. and other foreign countries, I can plan to harm a foreigner and not be charged with any crime under U.S. law.
As such I do execute my plan on that nationality's soil or territory I can be detained, arrested, jailed/ put in prison, tried, and penalized under such country's laws.
Should I execute such a plan against a foreigner on U.S. soil or territory I can be arrested, etc, etc, under applicable U.S. Laws.
Should I plan and/or execute such a plan to cause harm to another American, again depending on what country I am in, and applicable foreign country's international agreements with the U.S. or should I plan such attack on U.S. soil or territory I can be fully prosecuted under applicable U.S. Laws.
Things like (if any): extradition agreements, friendly informal agreements, various international laws and any other reciprocating agreements, etc., etc., etc., variables come into play as to jurisdiction, etc., etc., etc..