Comment Re: More than one Meaning (Score 0) 85
No it's not. You conveniently left out another definition of conscientious:
careful and painstaking; particular; meticulous; scrupulous.
conscientious application to the work at hand.
In re: your question, the person would pay attention to the details of harming someone as they were instructed. For example, a mob hit. They wouldn't just walk up to the person in broad daylight with hundreds of people around and shoot/stab them (though this has happened). Instead, they would observe the target, find out their routine, where they live, then, when that person is alone and it is dark, go out and kill them. The hitman was conscientious in how they did their task. They paid attention to the details and did their job well.
English isn't your first language, is it?