Abby Tyler, 15, died about 11:15 a.m. EDT at a Spartanburg hospital after fighting for her life for two days, Cherokee County Coroner Dennis Fowler said.
Tyler was wounded and her father was killed Thursday as they worked to close the Tyler Home Center near downtown Gaffney.
County Sheriff Bill Blanton said investigators believe the killings are linked and the search is on for a suspected male serial killer. An 83-year-old mother and her daughter were shot to death Wednesday, and a 63-year-old peach farmer was found dead at his home a week ago.
Blanton said all the victims were shot, but he would not say how the deaths were linked. The shootings all occurred within about 10 miles of each other in Cherokee County, a rural community of 54,000 people set amid peach orchards and farms some 50 miles west of Charlotte, North Carolina.
The spree had alarmed residents canceling Independence Day holiday plans and arming themselves. The sheriff has warned door-to-door salesmen to stop knocking and anyone who breaks down on the county's rural roads to wait instead of walking to a house for help because he worries "people are going to start shooting at shadows."
The killings began a week ago Saturday when the wife of 63-year-old peach farmer Kline Cash found him dead in their home. Then last Wednesday, relatives found 83-year-old Hazel Linder and her 50-year-old daughter, Gena Linder Parker, bound and shot to death in a separate shooting at Linder's home.
Dozens of local, state and federal investigators were assigned to the case when the killings were linked. But a day later, the killer struck again, less than a half-mile from the sheriff's office serving as the headquarters for the investigation, killing 48-year-old Stephen Tyler and his daughter.
"We're knee-deep in the investigation," Blanton said Sunday. "There's fear and concern here and there should be concern."
Investigators have released a sketch of the suspect, saying he is in his 40s, tall, with salt and pepper hair. They think he is driving a silver 1991-1994 Ford Explorer.
By Associated Press Writer Mitch Weiss; AP Writers Jim Davenport and Jeffrey Collins contributed to this report from Columbia