A fight between best friends ended in a deadly stabbing, according to investigators.

Police say 59-year-old Patrick Griffin admitted to killing his best friend James Knapp Saturday night over an altercation. Griffin claims he acted in self-defense. Police say they found the knife with Knapp's blood on it.

Griffin appeared in Danbury Superior Court Monday on manslaughter charges.

James Knapp's family says their father went to Griffin's house in New Fairfield Saturday to watch the Kentucky Derby because Knapp was concerned about his friend being alone.

Police say as the night went on and intoxicating substances played a role. Knapp's family believes Griffin was struggling with substance issues. Police say Griffin stabbed Knapp in the chest and Knapp later died at the hospital.

"Jim always tried to see the good in people and didn't want anyone struggling to be alone. It's heartbreaking that his life ended like this," said Knapp's son Ryan, who is a Newtown councilman.

Knapp, 65, lived in Sandy Hook and was a former teacher at Pomperaug Regional High School in Southbury.

"Our family is devastated by the tragic and untimely death of my father. My brother and I had just been with him. The day he passed we had been talking about his plans to enjoy more time with his grandchildren," Knapp told News 12 Connecticut.

Griffin's wife told News 12 Connecticut she's stunned by the incident. She says she has no words.

Griffin is being held on a $750,000 bond. He is due back in court in two weeks.