Police investigations into the shooting of the nation's police chief more than nine years ago reached a major milestone last week with the arrests of four men, including a former police officer. Around 8:30 a.m. on March 30, 1995, a gunman fired several shots at Mr. Takaji Kunimatsu, then director general of the National Police Agency, wounding him seriously as he was leaving his Tokyo home for work.

The former police officer who was arrested, Mr. Toshiyuki Kosugi, was a follower of the Aum Shinrikyo cult, which carried out a sarin nerve-gas attack on the Tokyo subway system on March 20, 1995. Mr. Kunimatsu was shot following police raids on cult facilities. The other three suspects were all senior Aum members.

The shooting incident, one of the most serious criminal cases involving the terrorist cult, is still shrouded in mystery. According to investigators, Mr. Kosugi confessed to the shooting in 1996 but was not arrested at the time because of a lack of evidence. It remains unclear whether the cult guru Shoko Asahara was involved. The arrests of the four men Wednesday, however, raise hopes of a breakthrough.