Japanese prosecutors investigating Prime Minister Noboru Takeshita's links to a political bribery case lost a key witness Wednesday when Takeshita's former top aide committed suicide, police and news reports said.

Ihei Aoki, 58, slit his left wrist and hanged himself with a necktie suspended from a curtain rod in the bedroom of his Tokyo apartment a day after Takeshita announced he would resign over the political scandal, police said.Aoki's involvement in the "Recruit-gate" bribery scheme was the first indication of Takeshita's own part in the scandal.

"We spent more than 30 years together, and it is very regrettable," Takeshita said of Aoki's death.

Takeshita was handed a note informing him of Aoki's suicide as he attended a funeral for former Agriculture Minister Takao Kameoka, who died last month of heart disease, government-supported NHK televison reported.

Aoki resigned as Takeshita's secretary in 1986 but continued to serve as his chief fund-raiser.

The Japanese media suggested that Aoki committed suicide to avoid facing questions about the scandal. "Annoyed by Recruit questions?" said the headline of the daily Tokyo Shimbun.

Aoki had been questioned by prosecutors investigating the political scandal, Yusuke Yamaguchi of the Tokyo District Prosecutor's Office told the Kyodo news service.

Masayoshi Ito, 75, a leading member of the ruling party and former foreign minister, reportedly is the leading candidate to replace Takeshita.