Tokyo District Court on Wednesday sentenced a former employee of drugmaker Daiichi Sankyo to 16 years in prison for the murder of his wife by methanol poisoning in 2022.

Presiding Judge Iichiro Sakata said that the use of methanol in the case was "more difficult to detect than other killing methods, highly planned and ruthless."

Prosecutors had sought a prison term of 18 years for the defendant, Keisuke Yoshida, 42.

In his lay-judge trial, the defense side argued that the wife may have taken methanol by herself so as to end her life. However, the court found this to be highly unlikely as it would be unnatural for her to do this and leave behind her beloved son.

The court pointed out that it was easy for Yoshida to obtain methanol as he routinely handled it at work. As for a motive for the murder, the court said it was natural for him to harbor strong frustration with his wife as their relationship was so bad that they were living separate lives under the same roof.

According to the ruling, Yoshida had his then-40-year-old wife, Yoko, take in methanol at their home in Tokyo's Ota Ward between Jan. 14 and 15, 2022, resulting in her death from acute poisoning on Jan. 16 that year.