The Kyoto Prefectural Police said Friday that traces of cyanide had been detected on a bag found in a plant pot thrown out last summer by the alleged "black widow" arrested last month on suspicion of murdering her spouse last December.

Police examined the pot Chisako Kakehi, 68, had asked a recycling company to dispose of along with other household items at her home in Muko, Kyoto Prefecture, and discovered a small zipped plastic bag tainted with cyanide.

They said an autopsy confirmed cyanide as the cause of 75-year-old Isao Kakehi's death because two or three times the fatal dose of the poison was found in his body.

The results have led police to believe Kakehi killed her previous unmarried partner the same way, as traces of cyanide were also found in his body. The 71-year-old man, from Kaizuka, Osaka Prefecture, died in March 2013, before the suspect married Isao Kakehi in November last year.

The prefectural police said the evidence raises the likelihood that Kakehi buried the cyanide in the planter to hide evidence. The woman, however, has denied any involvement in her husband's death.

"If someone finds poison it will mean someone has fabricated evidence," Kakehi told reporters when she was interviewed before her arrest.

She also muttered: "Is (cyanide) really so easy to get?"

Investigators believe she may have inherited about ¥1 billion from a string of late partners, using most of it for investments.