More than a third of the murders, attempted murders and fatal assaults involving members of the same family in 2014 were motivated by "fear of the future," such as concerns about caring for elderly relatives or managing financial hardship, according to police data released Monday.

Parents were the most frequent victims, according to the first detailed breakdown of such cases for a full year. That's an indication that many people are unable to cope with caring for their aging parents, officials said.

Such cases may increase in the future, as many people in fast-graying Japan continue to face difficulties in securing a slot in nursing care facilities, support groups for caregivers warn.