Photo/IllutrationPolice found the bodies of three senior citizens at this home in Tsuruga, Fukui Prefecture. (Mizuho Morioka)

TSURUGA, Fukui Prefecture--A 71-year-old woman who snapped from emotional exhaustion after nursing her ailing husband and in-laws for years and killed all three is now in police custody.

Masako Kishimoto, described as "a model daughter-in-law," was arrested in connection with the slayings.

Her case highlights the potential tragedy looming in families where senior citizens are often looking after elderly family members with little or no outside assistance.

Police were called to Kishimoto's home after she told another relative that she had killed her husband, Takio, 70, her father-in-law, Yoshio, 93, and her mother-in-law, Shinobu, 95. Masako told police she strangled all three.

The four had been living together in the same home for about a decade and neighbors said they often heard Yoshio and Shinobu praising Masako as the "best bride in the community."

But another woman neighbor also heard from Masako about how exhausting it was to care for the three other family members. Yoshio and Shinobu rarely left the home and could no longer consume solid foods. Masako also assisted them in using the toilet.

Her husband suffered a stroke a few years ago and was unable to provide any help.

The 72-year-old neighbor noticed that Masako this summer did not appear to be her self. Masako confided to her friend that she was finding it increasingly difficult, both physically and psychologically, to keep shouldering the burden.

About a week before the three were found dead at their home, the woman visited Masako to inquire about her well-being. Masako seemed troubled and complained about her own physical problems. When the woman suggested Masako call an elderly-care manager, Masako agreed, but apparently did not pursue that option.

Others who knew the Kishimoto family were stunned to learn that Masako had been arrested.

An 88-year-old neighbor remembered Masako as a very kind woman who never complained.

"I never imagined something like this would happen," the woman said.

Shinobu used a day service facility once a week. An employee at that facility was stunned by the incident because Masako showed no outward signs of anything having changed in her circumstances.

The rapid graying of the Japanese population raises the possibility that more tragedies like this could occur.

The National Police Agency said that in 2018 there were 31 murder cases in which the motive was fatigue arising from having to care for loved ones, often for many years. Since the agency began keeping track of the phenomenon in 2007, there have been on average between 30 to 50 such cases annually around Japan.

A study in 2016 by the Ministry of Health, Labor and Welfare found there were 13.252 million households in Japan where all members were 65 or older. The figure represents one quarter of all households.

(This article was compiled from reports by Mizuho Morioka, Ippei Yaoita, Naoki Hirano, Yukiko Nagatomi and Haruhiko Yoshimura.)