Every single soldier is trained the same way , to work under their laws , under the command and to obey orders. If someone disobeys orders or does something that wasn’t part of his training then how can the instructors be charged ? If a driver kills someone through dangerous driver does his driving instructor get charged - soldiers aren’t trained to ignore orders and kill innocent people
And you can never ever tell how someone will react under true stress until they actually face it and you can’t do that in training
The culpable ones are the guys that pull the trigger illegally or the officer who order the trigger to be pulled illegally - not an instructor who teaches thousands of soldiers who 99% act within the law
On the issue of an instructor, or the author of the instruction, being prosecuted, its down to the quality of the training and the training material. I'm not saying anything either way on whether or not a prosecution is valid, only that instructors and instruction authors could be culpable if the instruction is deemed to be lacking. That has been the case for a number of years, further beefed up in 2017 with new legislation.
How someone reacts under stress isn't part of competence or culpability of the instructors.