FORT EDWARD, N.Y. -- Kevin Gonyea said out loud in Washington County Court that he strangled his grandmother, a 95-year-old woman who raised him, to death with a towel last July inside her Fort Ann home.

Gonyea, 50, took a plea deal, admitting guilt in exchange for a sentence of 15 years to life in prison. He was initially charged with second-degree murder, hindering prosecution and tampering with physical evidence.

Leona Twiss was found inside her Twiss Road home when investigators responded to a call about an unattended death..

"This was a mercy killing," said Greg Teresi, defense attorney. "This was a man who saw his grandmother deteriorating. Alzheimer’s and dementia. At the end of the day, he did it because legitimately didn’t want to see his grandmother suffer."

"Certainly anyone who’s had a loved one who suffered with the trials and tribulations of the golden years can understand it’s difficult to watch someone you care about suffer," Teresi said.

Gonyea and his wife, Melissa, moved from Florida to live with and take care of Twiss.

Back in November, Melissa pleaded guilty to hindering prosecution, tampering with evidence and offering a false instrument charges in exchange for testimony against her husband.

In court, Gonyea told the judge he suffers from bipolar disorder and was on medication for it at the time of the crime.

Gonyea also pleaded guilty to filing a false social security claim with his wife. He is due back for sentencing on February 23.