Two doctors indicted last year over the consensual killing of a terminally ill woman in Kyoto were served with fresh arrest warrants Wednesday for allegedly murdering a man, the father of one of them, police said.

Yoshikazu Okubo, 43, and Naoki Yamamoto, 43, are suspects in the March 2011 death of Yamamoto's 77-year-old father Yasushi in Tokyo, according to the Kyoto prefectural police.

The police also arrested Yamamoto's mother Junko, 76, for her suspected involvement. The police did not reveal whether the three have admitted to or denied the charges.

Yasushi Yamamoto had been hospitalized in Nagano Prefecture at the time for a mental disorder, but the suspects had him discharged on March 5, 2011, for transfer to a different hospital, according to investigative sources.

He died the same day although his condition had been stable shortly before the transfer, the sources added.

The police discovered emails between the suspects suggesting they attempted to kill Yasushi Yamamoto, the sources said.

His body was buried without an autopsy or inquest.

The two doctors were indicted in August last year for allegedly giving a 51-year-old woman suffering amyotrophic lateral sclerosis, also known as Lou Gehrig's disease, a lethal dose of a sedative drug at her home in Kyoto in November 2019. Before her death, the woman had transferred money to Naoki Yamamoto's bank account.