Morikazu Tanaka, a prosecutor-turned-lawyer who was known for his underworld connections, died Saturday morning of stomach cancer at a Tokyo hospital, people close to him said. He was 71.

Earning his prosecutor's badge in 1971, Tanaka worked in the special investigative squads of the Tokyo and Osaka public prosecutor's offices before becoming a lawyer in 1988.

As a lawyer, his clients included leading members of the Yamaguchi-gumi yakuza syndicate, among other underworld figures, and "sokaiya" corporate racketeers.

In 2000, he was arrested by the special investigative squad of the Tokyo Public Prosecutor's Office for defrauding an oil sales company of ¥18 billion in 1996, an incident that developed into a major political bribery scandal. A court found him guilty of conspiring with Heo Young Joong, who was also convicted over the collapse of trading house Itoman Corp.

While on bail, Tanaka wrote a best-selling autobiography published in 2007 titled "Hanten" ("Inversion") depicting his eventful life.

He was handed another prison sentence in 2010 for a separate fraud case and was diagnosed with stomach cancer the following year while in jail.

After his release on parole in 2012, Tanaka worked to spread the teachings of Confucius. He was hospitalized earlier this year when his cancer returned.