A 78-year-old man was discovered dead with a pillow over his face inside his Upper East Side apartment Wednesday night, police said.

Christopher Cooley was found on the couch of his East 64th Street home about 8 p.m. by a horrified building worker who was asked to check up on the elderly resident by his concerned family members.

“All I saw was his legs. I was calling to him ‘Mr. Cooley, Mr. Cooley,’” said building super Ray Kasaj.

The 11th floor resident was declared dead by authorities shortly after – who also discovered blood on Cooley’s shirt and a living room in disarray.

A broken lamp lay by his feet, along with shattered glass nearby. Cooley had $192 in his right pocket and was still wearing his wrist watch, police sources said.

Investigators also determined the deadbolt to Cooley’s pad was locked, ruling out a break-in, police sources said.

Earlier in the evening, Cooley’s sister became worried after repeated failed attempts to get in touch with him, police said.

That’s what led to the grim discovery, which Kasaj said he won’t forget anytime soon.

“That is something that stays with you. I still have the smell in the pit of my stomach,” said Kasaj.

Police are still investigating the mysterious death and the city’s Medical Examiner will determine what caused it.