Tokyo District Court Judge Kiyoshi Kimura said former Aum Shinri Kyo, or Supreme Truth, cult member Yasuo Hayashi, 42, deserved the sentence because he released the largest amount of poisonous sarin gas in the attack, which claimed 12 lives and injured thousands.
Prosecutors charged that Hayashi was directly responsible for the deaths of eight people by carrying three plastic bags of the deadly gas onto a packed commuter train. He released the gas by puncturing the bags with the sharpened tip of an umbrella.
Hayashi was also charged with other crimes, including taking part in a separate gassing the previous year.
Hayashi was the second cult member to receive the death penalty. The other, Masato Yokoyama, has appealed.
Media reports quoted Hayashi's lawyers as saying they would seek an appeal.
"This morning I prayed that he would get the death penalty. I am satisfied," NHK quoted a parent of one of his victims as saying after the ruling.
Hayashi had told the court that he believed he would be sentenced to death. "Whatever my motives may have been, I think I will get the death penalty," he told the court in February.
After the subway attack, Hayashi went on the run, living in hideouts across the country for about a year and a half before being arrested in one of the southern Okinawa islands.
While a fugitive, he took part in another gas attack -- which ailed -- at a busy Tokyo train station, setting rumours swirling that the "murder machine" was set to commit more acts of violence.
Hayashi, who had travelled around the world in search of spritual guidance, found it in the teachings of Aum founder Shoko Asahara, and joined the cult when he was 30.
But what he did in the cult was far from being spiritual.
He is believed to have been a core player in the group's illegal activities, which ranged from harassment of former members and wire-tapping their homes to actual killing.
In the 1994 gas attack, Hayashi was accused of helping to build a car to release sarin gas in a residential area.
Seven died in the attack, which was carried out near a dormitory for judges and court officials. Aum is believed to have targeted judges who were handling a lawsuit involving the cult.
Hayashi's lawyers argued he was not aware of the danger of sarin gas and was only following orders -- under the threat of death -- from cult guru Shoko Asahara.
Asahara, whose real name is Chizuo Matsumoto, remains on trial for masterminding the Tokyo subway gassing and for more than 16 other charges.
Asahara's trial, now in its fifth year, promises to go on much longer in what has come to symbolise the nation's notoriously snil-paced court system, with some legal experts saying it may well take over 15 years for a final verdict.
While most of Aum's leaders are now behind bars, the cult still remains active, prompting the government to place it under surveillance in February for three years. The move allows authorities to inspect all its sites.
For its part, the cult has changed its name and insists that it is now a benign religious group.
In the past, Aum preached the world was coming to an end and that the cult must arm itself to prepare for various calamities.
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