An 83-year-old man and his 84-year-old wife were found shot to death inside their Cleveland, Tenn., home on Sunday in what police say appears to be a murder-suicide.

The couple's son found Max and Sue Liner dead inside their home at 515 Springhill Drive around 11:20 a.m. Sunday, according to Cleveland police.

Police did not say who they believe was the shooter in the deaths, but did confirm that one person's wounds appeared to be self-inflicted.

Both Max and Sue Liner suffered from health issues, public information officer Evie West said. She did not disclose any specific health conditions and said the investigation into the deaths is ongoing.

The pair had owned the home since 1975, property records show.

There is no national database of murder-suicides in the United States, but the Violence Policy Center, a nonprofit organization focused on reducing gun violence, periodically collects and analyzes reports of murder-suicides during six-month spans.

Most recently, the center analyzed murder-suicides that happened during the first six months of 2014. In that time period, the researchers found 282 murder-suicides that resulted in 617 deaths, according to its report.

A full third of those murder-suicides involved a murderer who was age 55 or older, according to the report. That's higher than past years — in 2001, only 21 percent of murder-suicides involved a murderer age 55 or older.

Over time, the Violence Policy Center's reports suggest murder-suicides are on the rise among the elderly. In 2005, the percentage of examined murder-suicides that involved older adults rose to 23 percent, then to 27 percent in 2007 before decreasing to 25 percent in 2011.

Studies have shown spousal murder-suicide among older adults is associated with declining health, an anticipated separation or move, and undiagnosed depression in the husband, according to a 2010 study published in The Journal of American Academy of Psychiatry and the Law.

Men are much more likely to be the aggressor in murder-suicides than women, according to the Violence Policy Center. Researchers found men were the murderers in 89 percent of the murder-suicides they examined during the first six months of 2014.

There were 10 murder-suicides in Tennessee during that time period, the study found.

Contact staff writer Shelly Bradbury at 423-757-6525 or with tips or story ideas. On Twitter, follow her @ShellyBradbury.