HERNANDO COUNTY, Fla. (WFLA) — More than 40 years later, detectives have finally confirmed the identity of a third set of remains discovered in Hernando County.

Theresa Caroline Fillingim was reported missing by her sister in 1980. Her remains were found a year later on land where a serial killer once lived.

The cold case detective credits advances in technology with being able to identify Fillingim four decades later.

“That’s the last unanswered question now with that victim,” cold case Detective George Loydgren said.

Investigators say Fillingim vanished without a trace May 16, 1980 in Tampa – just a week shy of her 17th birthday.

“She was abducted, I’m confident, on that day and then was murdered,” Loydgren said.

In 1981, nearly a year later, Hernando detectives found four sets of human remains at a Spring Hill home belonging to the family of convicted serial killer Billy Mansfield. At the time, they identified two of the victims.

Within the last year, they’ve identified the third as Fillingim. The cold case detective for the Hernando County Sheriff’s Office reached out to her sister last summer.

“Sad in the sense that you’re giving somebody the sad news that their loved one is deceased, but it’s a positive and happy for me because I’m instrumental in bringing her home,” Loydgren said.

WFLA spoke with Fillingim’s sister Margaret Johns in an exclusive interview Tuesday.

“Forty-two years is a long time,” Johns said. “Life is short. It can be even shorter for some and watch your back, because there’s a lot of bad people out there that’ll do a lot of bad things to people.”

Johns says Theresa was the baby of the family.

“She was a little princess,” Johns said. “Very nice, very easygoing.”

Johns says many of their family members died without knowing what happened with Theresa. The news gives the rest of them some closure.

“It gives me peace because I know I didn’t lose her – that she was taken,” Johns said.

Johns wants families waiting for answers about missing loved ones to never give up hope. 

“Now I can stop looking,” Johns said.

The Hernando County Sheriff’s Office says several agencies helped in identifying Fillingim and bringing peace to the her family. Those include the University of North Texas, Dr. Erin Kimmerle and Kelsee Hentschel Fey with the Forensic Anthropology Department of University of South Florida, N.A.M.U.S., the Fifth District Medical Examiner’s Office, Cape Coral Police Department, Longmont Police Department in Colorado, Tampa Police Department and Parabon.