KOBE (Kyodo) Police investigating the torching of two telephone dating clubs in March 2000 have arrested a woman who was managing rival shops at the time and served warrants on three men on suspicion of murder and arson, investigators said Friday.

The blazes, set with firebombs on March 2, 2000, at two Rin Rin House shops in Kobe's Motomachi district killed four customers.

The 65-year-old woman, arrested Thursday, was identified as Kayoko Nakai, who allegedly sought someone to torch the establishments.

On Friday, police served new warrants on arrested accused drug trafficker Akihiro Sakamoto, 45, Kazuhiro Nakane, 42, and Yoshihisa Nakamoto, 52, all for allegedly ordering the torching. Police said they suspect Sakamoto was the leader.

The three men are already in custody on unrelated charges.

Police said Nakai was running two telephone dating clubs in Kobe at the time. The Rin Rin House chain was growing popular quickly and had four outlets competing with Nakai's establishments.

Investigators believe Nakai felt threatened by the advance into Kobe of the major phone dating club chain, and offered Sakamoto more than 10 million yen to make the attacks.

All four have denied being involved in the deadly torchings, police said.

The March attacks left four customers dead from carbon monoxide poisoning and four others, including employees, with injuries.

Later in the year, police arrested heavy-machinery operator Kazuyuki Sano, 44, and an unemployed man, Shinya Kameno, 30, on suspicion of arson.

The Kobe District Public Prosecutor's Office charged the two with arson but later added murder and attempted murder after deciding they were "consciously negligent" -- aware of the consequences of the firebombing but did it anyway.

Another suspect, Kenichi Hori, 37, who is believed to have been a driver, is at large and on a wanted list.