A father who killed his mentally disabled adult daughter was convicted of murder and sentenced to three years in prison, a Daegu court said Thursday, citing mitigating circumstances including the decades of care he provided for the victim.

The defendant, in his 70s, suffocated his 40-year-old daughter at his former wife’s home in Daegu, about 240 kilometers southeast of Seoul, at around 9 a.m. on Oct. 23. According to the court, he attempted to quiet her down as she was making loud noises, saying, “Please be quiet, it’s difficult for me, too. It’s difficult for your mother, so please be quiet.”

He then covered her mouth and nose and strangled her.

The man had been living alone after his divorce but continued to care for his daughter at his ex-wife’s home. Investigators said he committed the crime out of frustration, as he no longer felt able to care for her, in part because of severe vision loss.

“The defendant devoted himself to caring for the victim for 34 years and appears to be suffering considerable mental distress following the crime,” the Daegu District Court said in its ruling, adding that murder cannot be justified under any circumstances.