I doubt that he would be prosecuted for terrorism in any other western democracies, it seems to be part of the USA prosecution habit of stacking up as many charges as possible, combined with the very broad anti terrorism laws after 2001.

If prosecuted as a murder, a jury trial would happen in a bunch of countries: https://www.nolo.com/legal-encyclopedia/do-countries-the-jury-trial-system.html Imo you assume wrong in this case.