The suspects can be sentenced a death penalty in Japan, even when they are brainwashed to commit felonies.
There were famous cases for believers of Aum cult, those eventually got out from the entrapment and realized their wrong conducts, though it was too late as they even executed a terrorist act harming thousands of people at Tokyo subway system. They killed tens of people including this terror, therefore many of them were sentenced a death penalty in the end.
This whole crime was conspired by the cult leader and the number two might have a critical role as well, though he was killed in the public eyes before his arrest, while their apprentices were the ones to really commit murders by their hands. Even though some of them were totally brainwashed, they could not avoid the death penalty, implying the brainwash is not necessarily a plausible explanation to avoid the responsibility.
They could not have discerned the right from the wrong under the mind control, deviated from the social norm, though they had realized their act was illegal and not acceptable to the society. They fully noticed that they would be punished once it was known to the justice system, whose recognition proved that they were responsible for their conducts.
This rationale holds true to this Awaji murder case stabbing to kill five people under the brainwash through the electromagnetic wave. He actually knew what he had done that it was the murder, prosecutable as such.
The judge dismissed the claim that he was brainwashed, as he was not an important figure to the overall society. It is partly true but does not explain the intelligence activity as a whole. This judge assumes that he was not a target of the anti-personnel operation as he cannot affect the overall Japanese society, while he can be targeted as a subject of the anti-society operation.
It is an operation to create a social disorder, which is one of the ways to influence on their targeted countries and people out there. The mass murders have been actually created for this purpose, as the social unrest provides the leverage to control the targets. It might be an intimidation to coerce the cooperation or might be to overthrow the existing government. In any way, the murder is one of the methodologies which the intelligence community conducts for their operation, which has been extended to brainwash the subjects to commit it without notice of their involvement through the electromagnetic capability.