It was critical to understand why the Japanese police intelligence should have covered up the North Korean involvement for those cases. The simple answer is that there was a deal between them, though it is still unclear what the nature of this deal. There were several possibilities for this reason behind.
The money was an important component of this deal, as there was a Korean won coin left behind the scene as well as the North Korean army badge. It basically implied that the North Korean spy blackmailed the Japanese police insider to reveal the money related issue.
There was a deal related to the money occurred before this shooting in 1995 and the pachinko concession was the most likely incident as the police took over some shares from North Korea between 1985 and 1989.
All of those suggested there was a man in power who could control an investigation of the Japanese police, though could not intervene a command of the director general. There were two possibilities of this individual, one was that he was a high-ranking officer, but not one of the main leaders at the national headquarter at that time, meaning he was one of the local police chiefs. Another was that he was an influential ex-officer of the police department, highly likely an ex-director general.
There were several names for these probabilities, not so many, and moreover, they have belonged to the same factional line in the police department, career police intelligence officers related to the covert team, getting a concession from the North Korea. The head of investigation division at the Tokyo metropolitan police at that time was one of their subordinated members.
There was another angle of this issue that the police intelligence was taken over by the left sympathizer around the same time. They were university students in 1960s when the Marxist student movement was peaked in Japan. Their political ideal was shared by North Korea, implying that they were not just a simple sympathizers connected by the money.
That was why I was framed to work together with one of the Aum fugitives, as his runaway was planned by the intelligence covert team and the same team had tried to push me to the extremist activity to create a successor of their movement.
The police cover-up was mainly decided by the North Korean sympathizers who have been connected by the pachinko concession, but there was another reason that the left radicalized police officers wanted to support North Korea with the political reason as they have shared the same socialist ideal.