Police on Tuesday arrested a man in his 20s on suspicion of aiding the gangster who has admitted assassinating Nagasaki Mayor Itcho Ito.
Nagasaki Prefectural Police said Masaki Yamashita, the second suspected accomplice under arrest over the mayor's killing, was a driver for mobster Tetsuya Shiroo, 59, who was arrested at the scene of the assassination.
Yamashita is suspected of monitoring Ito's movements at places other than his election campaign office. The April 17 shooting took place on the street outside the office.
On Sunday, Hiromi Ogawa, 60, was arrested. Police said he has admitted driving Shiroo to the scene of the attack outside JR Nagasaki Station shortly before Ito, 61, was gunned down while campaigning for re-election in the April 22 mayoral poll.
Police said Yamashita told them he was a lookout but did not think Shiroo would kill Ito.
Police believe both Yamashita and Ogawa knew Shiroo was planning to murder the mayor and said they will question the two suspects about the shooting.