A friend went to check on Holmes early Thursday morning after not hearing from him in days and called police after arriving at the house.
Police said the 68-year-old man had signs of blunt force trauma to the head.
Holmes grew up in Plano's Douglas neighborhood and has lived in the same house for more than 50 years.
"I would be better off accepting what happened if he died from a heart attack or stroke or just natural causes. But murder? Who would want to do that?" said Holmes son, Kerry.
Friends said Holmes was always walking around the neighborhood, waving to people. Their suspicions were raised when they didn't see him for a few days.
"You couldn't tell me in a thousand years that Sherlock would get killed, that someone would go in there and murder Sherlock, do something terrible like that to him, because he wasn't that type of person, you know?" said Gene Drake, an old friend of Holmes.
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Friends, family and other neighborhood residents gathered Thursday near Holmes' home to console each other.
Jeanette Hunt said her friend was always cheery and willing to help. She said she can't believe she didn't get to tell him goodbye.
"I'm not going to see him pass by the house, and I'm not going to see him come over and ring the doorbell. I'm not going to see him," Hunt said, before burying her face in her hands and crying.
The Collin County medical examiner is determining the cause and time of Holmes' death.
Anyone with information about his death should call Plano police at 972-941-2445.