The Hunted

Paul Racine, a computer-chip executive from New York, is on a business trip to Nagoya. He meets Kirina in the hotel lounge, and they have a one-night stand. Kirina is approached by Kinjo and two ninjas. Kirina shows no fear and Kinjo, the leader of a cult of ninja assassins and grants her final wish by showing his face. Paul returns and hides in the foyer while calling the police. When Kinjo decapitates Kirina, Paul tries to come to her defense and then tries to flee. Enraged that someone has seen his face, Kinjo's men stab Paul, hit him with a poisoned shuriken and slash his throat, leaving him for dead.
Paul awakes in a hospital room, but his claims of seeing Kinjo are met with disbelief by the police. Lieutenant Wadakura dismisses the allegation and suspects that the murder is the work of a Yakuza syndicate. Paul is approached by Ijuro Takeda, an expert on the cult and Kinjo. Paul discovers that Takeda is the last in a samurai line and has a score to settle with Kinjo. The ninjas attempts to murder Paul at the hospital, killing several hospital staff and police officers, including Wadakura, but Paul escapes. Takeda and his wife Mieko subsequently take Paul to their family's stronghold, located on an island several hundred miles away. Leaving the city, Takeda uses Paul as bait to draw Kinjo out, leading to a battle on the train where several passenger cars of innocent people are slaughtered by the ninjas. Takeda and Mieko defeat the attackers, but Kinjo was not among them. The ninja leading the attack was Junko, Kinjo's lover, giving Kinjo motivation to kill Paul and Takeda.
On the island, Paul spends time with the drunken blacksmith Oshima, who is constructing a sword for Takeda, and the old man teaches him about smithing and swordsmanship. Mieko explains the history of the two clans' conflict and the samurai concepts of courage and honor. Mieko is sympathetic toward Paul, the polar opposite of her husband, although she remains loyal to Takeda.
Kinjo decides to find out who hired his clan to murder Kirina. The man he finds, Nemura, is a powerful Yakuza figure who bought Kirina from her father, then ordered her death when she left him after years of servitude. Kinjo, disgusted that he killed an innocent woman over such a petty grievance, kills the man.
Three weeks later, Takeda's new sword is ready, and Paul's injuries have healed. When Paul announces that he wants to leave the island and return home to New York, Takeda has him imprisoned and sends a message to Kinjo telling him Paul's whereabouts. Takeda's inexperienced samurai are overwhelmed by the hordes of ninjas who arrive, but Takeda gets the duel with Kinjo he wants. Kinjo stabs Takeda through the torso; Takeda in turn stabs Kinjo in the leg, but soon dies.
As Kinjo is about to kill a helpless Mieko he is caught off-guard by Paul, whom Oshima had released on Mieko's instructions. Paul stabs Kinjo in the arm, but is armed with only a sword he barely knows how to use. With his newfound skills, a lot of luck and the assistance of a wounded Mieko, Paul decapitates Kinjo. Paul, Mieko, and Oshima head up the hill toward the castle.

Question: Who work does Lieutenant Wadakura suspect the murder of?
Answer: Yakuza syndicate