The top scientist of a cult suspected in a deadly nerve-gas attack on Tokyo's subways died Monday of stab wounds, dealing a potential setback to police investigating the sect.

The slaying of Hideo Murai, one of Aum Shinri Kyo's most visible leaders, jolted a nation already shaken by a month of terrorist attacks.Murai, who was in charge of the cult's secretive large-scale experiments with chemicals, was stabbed Sunday night as he left its Tokyo headquarters. He died several hours later at a hospital.

The stabbing was carried out in front of television cameras, and all major networks devoted their morning programming to the attack, some repeatedly showing slow motion video of a knife plunging into Murai's side.

Police identified the attacker as Hiroyuki Jo, 29, a South Korean national with Japanese residency. He is unemployed and has no permanent residence, police said.

The attacker pushed through a throng of reporters staking out the cult's Tokyo's headquarters and slashed repeatedly at Murai with a kitchen knife. After the stabbing, he dropped his bloody knife on the pavement and was arrested.

"After seeing TV and newspaper reports, I thought I had to do something," Jo reportedly said. "I wanted to strike at the leadership of the Aum Shinri Kyo."

Police said Jo belonged to a small rightist group called Protectors of the Land of the Gods.

The South Korean government asked Japan to protect its embassy and other diplomatic facilities in Japan against possible cult retal-i-a-tion.

Murai, 36, was believed to hold crucial information about whether the cult was involved in the March 20 subway attack, which killed 12 people and sickened 5,500.

Police have made no arrests and have not officially identified any suspects.

Japanese media reported during the weekend that police were planning to round up top leaders of the cult - including Murai and cult founder Shoko Asahara - for ques-tion-ing in connection with the subway attack.