There were basically terrorists to target helicopters of Japanese defense force in Japan. It should be the left extremist who has been sabotaging the Japanese defense and who has the capability to conduct the electromagnetic manipulation.
Although, it is apparent that they have had no capability to develop this technology by their own. Some government organization should have provided them to run the electromagnetic operation to sabotage the Japanese government.
I saw a bird controlled by the electromagnetic wave in 1993, which implied this function could be already established in 1980s. It also meant that the left extremist might get this device from the Soviet Union. However, that control I saw was conducted by the Japanese police intelligence at that time.
The Japanese intelligence definitely provided this technology to their assets for their covert operation, which includes the left extremist, or more precisely saying, the majority of their assets are members of the left extremist. Considering the timeframe, this device is used for the attacks against helicopters belonging to the Japanese defense force.
In the end, there were two possibilities that the left extremist independently fell them down with the electromagnetic technology provided by the Japanese police intelligence or the intelligence officers ordered to do so, including an implication. In either way, the left extremist was the main perpetrator, which is openly or implicitly supported by the police intelligence, which should also share the responsibility in any way.
Having said that, there is a slight possibility the attack was executed by the device which was not provided by either the CIA or the Japanese police intelligence. Although, it was still almost surely conducted by the left extremist and they should be spies of the intelligence community in any way.