It is a general issue that some of the criminals are immune from prosecutions when working as an asset to the intelligence organization. In the police operation, they have often hired rats to know the detail of criminal activities of others but themselves. The criminal spies can access easily to other criminals who were eventually arrested in this scheme.
However, this immunity created a chance for any crimes with free-hand. This issue should be critical enough and some of the murder cases were immunized as well.
There were other types of crimes created in this scheme that the police asked their rats to create a crime. There were many cases in Japan that the police department confiscated drugs and weapons prepared by their rats.
The same structure has been seen at the left extremist in Japan. Some of their members have been hired as spies to the police intelligence, who worked to frame other members of the same extremist group.
On the other hand, their sabotages were immunized as they worked as spies. In the end, the extremist has been radicalized to conduct violent crimes with an immunity as their nature was not changed even after they work for the police.
The police has had their own logic that their spies can proceed a career with a successful sabotage operation, which should lead more control over this specific terrorist group. On the other hand, the extremist spy can conduct an illegal operation without a worry to be caught.
This relationship is also seen between the CIA and their asset, both of those have immunized from Japanese legal system. They cannot be prosecuted even when they have conducted many illegal transactions including an insider trading. Or, more precisely, they are exempted from the official prosecution. The CIA has enough capability to negotiate every issue under the table, which provides them de facto immunity.
There were several investors who had conducted numerous illegal transactions, which was found in a course of the insider inspection in 2012. However, nobody was arrested within their circles. I heard this story at the almost end of their industry-wide operation because some of the officers of the CIA and Japanese police were so mad at this untouched outcome.
I have been fully monitored by many authorities, hence they let other parties know unacceptable crimes were left at large. This conversation was recorded and heard by lots of people, but still, they would not have arrested. There was just one reason why they were not prosecuted; they had worked for the CIA.