Police on Wednesday served a second arrest warrant for murder to an elderly woman who is already charged with poisoning her husband with cyanide and is suspected in the deaths of several other former partners.

Chisako Kakehi, 68, is suspected of killing Masanori Honda, 71, from Kaizuka, Osaka Prefecture, with whom she was in a common-law marriage. Cyanide compounds were detected in samples of Honda's blood, the sources said.

Police are looking into the case as a possible bid by Kakehi to inherit Honda's wealth, which amounts to tens of millions of yen.

Honda fell while riding a minibike on a street in Izumisano, Osaka, and died in hospital in March 2012, the sources said.

An autopsy found that he had died from heart disease. But Kakehi is suspected of administering a dose of cyanide to Honda before his accident, they said.

Kakahi denies being involved in his death, police said.

Investigators found that Honda had introduced Kakehi to his friends as his "fiancee" from autumn 2010 through winter 2011. He wrote her into his will, and she eventually received his property and savings.

Last December, she was charged with killing her 75-year-old husband, Isao Kakehi, who died at the couple's home in Muko, Kyoto Prefecture, on Dec. 28, 2013. They had married the previous month.

Last year, investigators found a small bag containing traces of cyanide in the soil of a plant pot she had tried to dispose of through a recycle service.

Kakehi is believed to have married or had relationships with six men since 2006, all of whom died within a few years of marriage or starting a relationship with her. Isao and Honda are among the six.

Kakehi was first arrested on Nov. 19 on suspicion of giving her husband at the time, Isao, a fatal dose of cyanide.