If you are told to kill someone by the person in front, you should not accept it, because you do not believe it is the right thing to do. You have your own internal ethical code which is basically against conducting anti-social behavior including the murder.
This is the whole point. The spies definitely crack this ethical code to make you believe to kill someone is a necessary measure. That is why the apparent voice sent directly to your brain is quite dangerous as there is a possibility you just believe it is sent from the supernatural existence.
Having said that, it is still hard for the operatives to convince you to conduct the murder, as it is still out of the most of ethical codes. There are people who believe the murder is one of the options, though the majority of religions denounce the fatal measure as unethical.
It is necessary for the operatives to crack the code and the apparent voice is the most efficient way to alter the subject’s thought. There might be a reason why you are triggered to commit felonies, even though you still believe it is a wrong thing to do. They manage to find it through a dialogue between the subject and the voice sent by the electromagnetic wave.
There is no right pathway for this manipulation as the personal belief system varies person to person, hence the spies made tries and errors, which is retrospectively left as the proof. In the murder case, the operatives eventually found the crack and that is why the perpetrator was manipulated to commit the crime.
There are many alternative ways to manipulate the subject with the electromagnetic wave. Twilight learning is another way to manipulate the subject under the REM sleep, which is more covert as the subject does not realize the existence of the voice sent from the outside.
The spies can send the voice similar to the inner voice, which is a weak form to manipulate the subject, especially for the brainwash to commit felonies, though it is still capable enough.
We should be noted that the most of manipulations are executed to find those cracks, which is the same for the traditional clandestine operation, and we should stick to our original ethical code, which secures us from the brainwash to become a murderer.