Japanese prosecutors said 39-year-old Masami Tsuchiya was the second most important figure involved in the gas attacks by the Aum Shinrikyo cult, after cult leader Shoko Asahara himself.

Tsuchiya, a chemist by training, headed the cult's drive to develop an arsenal of chemical weapons, including VX, mustard and sarin gases. The cult's aim was to spark an "Armageddon" in Japan by using the chemicals against an unsuspecting public.

The most serious of the charges concerned two separate attacks with sarin nerve gas. The first took place in 1994 in Matsumoto, 220 kilometers west of Tokyo, killing seven people and sickening hundreds.

The second and more spectacular was the coordinated release of sarin by several cult members in 1995, during rush hour in the Tokyo subway system. Twelve people died in that attack, and thousands were injured.

The cult killed at least one other person with gas in yet another attack.

The presiding judge, Satoru Hattori, ruled that Tsuchiya's crimes were premeditated and carried out with murderous intent. He said the cult would not have been able to carry out the attacks without Tsuchiya's direction.

It is not clear whether Tsuchiya, who often praised cult leader Asahara during his trial, plans to appeal. Ten other cult members sentenced to death before Tsuchiya's trial have appealed.

In Japan, death row prisoners whose sentences are upheld are not told their fate until the day of execution. Death sentences in Japan are carried out by hanging.

The trials of Tsuchiya and other senior Aum leaders have dragged on for years because of legal maneuvering by the defense and long lists of criminal charges involving huge quantities of evidence and testimony.