(CBS) RICHLAND COUNTY, S.C. - Police say a roll of duct tape found in the investigation of 15-year-old Gabrielle Swainson's disappearance had both the teen and her accused kidnapper Freddie Grant's DNA on it.
At a Friday press conference, Richland County Sheriff Leon Lott announced the DNA results and said he had not given up on finding Gabby and bringing her home safely.
According to CBS affiliate WLTX, Lott had said previously that investigators found pieces of duct tape with Gabbiee's blood on it at Grant's home in Elgin.
Gabrielle's mother, Elvia Swainson, also spoke Friday, thanking those who had contributed to the search effort and making a plea for the public's help.
"I have not given up," she said. "I'm believing until the very end that this is going to turn out well."
Authorities also announced that the reward for information regarding the missing teen is now $8,500.
Gabrielle was last seen about 4 a.m. on Aug. 18 as her mother left for work. Grant was charged with her kidnapping on Aug. 27, but police say he has refused to say anything. He remains in the Lexington County jail.
Elvia Swainson said she has sent letters to Grant in hopes that he'll give up information leading investigators to her daughter, but says has not gotten a response.
Complete coverage of the Gabrielle Swainson case on Crimesider