The death penalty has been sought for a 70-year-old Japanese woman, dubbed the "black widow". Besides being charged with the killing of her husband Isao Kakehi in 2013, Chisako Kakehi is also charged with the murders of two of her partners and the attempted murder of an acquaintance.

All the crimes were committed between 2007 and 2013 by giving the victims – all elderly men – drinks laced with cyanide.

Prosecutors made the request in their closing arguments at the Kyoto District Court on Tuesday (10 October) and described her crimes as "heinous and serious incidents that are rarely seen". They said that Chisako was "mentally fit" for the crimes that she executed and could be held responsible for them as they "were premeditated".

Her "cognitive function has not significantly deteriorated as shown in her psychiatric evaluation," they added, as reported by The Japan Times.

The woman's lawyer had earlier pleaded not guilty on her behalf. But Kakehi later admitted in court to poisoning and killing Isao. She had also explained her reasons behind the killing, saying, "I felt like (Isao) was discriminating against me (financially) in comparison to the last woman he was in a relationship with and I got angry."

However, she has now denied the charges again and pleaded not guilty. Her defence argued that Kakehi cannot be held responsible or stand trial due to the onset of dementia.

The defence will make its closing statements on Wednesday (11 October) and the court will subsequently hand out its ruling on 7 November.

Chisako was arrested in November 2014 and indicted after her fourth partner and husband, Isao, died in December 2013, a month after they got married. She was later indicted in connection with the deaths of the two other men.

It has been reported that Chisako, a native of Fukuoka Prefecture, was romantically involved with a number of men, 10 of whom are known to have died. She has an inheritance of approximately 1bn yen (£6.88m, $8.84m).