A 70-year-old Japanese woman, dubbed the "black widow", on Monday (10 July) admitted that she had poisoned her husband for money. Black widow is a term derived from the female spider that eats its partner after mating.

Besides murdering her husband Isao Kakehi in 2013, Chisako Kakehi is also accused of killing her two common-law husbands and attempting to murder a boyfriend, Japan Times reported. These crimes were all committed between 2007 and 2013.

Chisako was arrested in 2014 after her fourth partner died in December 2013 – a month after they got married. The post-mortem examination had found highly toxic cyanide levels in the blood of Isao Kakehi.

She had met the 75-year-old through a match-making site.

Her lawyers have pleaded not guilty on her behalf and maintained her innocence. But on Monday, when asked by prosecutors if she killed her husband, Chisako said that there was "no mistake" in fatally poisoning her husband.

When the prosecution asked her if she was admitting to poisoning and killing Isao and "are you making this admission while fully aware the punishment?" Chisako answered "yes".

The elderly woman, whose trial started on 26 June, has also explained her reasons behind the killing. She said: "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."

Chisako told the Kyoto District Court that she got the cyanide, which she used to kill her targets, from a business associate. "I got it from a business associate. I should have thrown it away when I got out of the business," she added.

But her lawyers have argued that the woman's testimony could not be trusted because of her "dementia".

"Since she is suffering from dementia, she barely remembers things that happened recently let alone the incidents," her attorneys said during the trial, which is expected to last until November.

It was said that Chisako was romantically involved with a number of men, ten of whom were known to have died. She has an inheritance of approximately 1bn yen (S$12.2m, $8.84m, and £6.88m).