Investigators made the link after finding 83-year-old Hazel Linder and her 50-year-old daughter, Gena Linder Parker, bound and shot to death Thursday in their home near Gaffney, Sheriff Blanton said at a news conference.
The home isn't far from a house where peach farmer Cline Cash, 63, was gunned down June 27. The sheriff said evidence makes it obvious that the killings are linked, but he refused to give details.
Authorities say the killer appears to be targeting women, although his first victim was a man.
Sheriff Blanton said the killer appears to have first spoken with Mr. Cash's wife about buying hay. She left and then came home a few hours later to find her husband's body.
"We think she may have been his intended victim," the sheriff said.
Investigators have prepared a sketch of a suspect and said they think he has been driving a dark blue van. They don't know exactly who he is or whether he is familiar with the area.
At least 30 investigators are working on the case, and Sheriff Blanton canceled all vacation and regular days off for his officers.
He said he wants anyone living in the area to be vigilant and call in any tips, large or small. He also asked any door-to-door salesmen to stop working until the case is solved.
Sheriff Blanton refused to say if anything was taken from the victims, whether they were sexually assaulted or why the killer might be targeting women. He said the killer didn't break into either home.