Skeletal remains found in Aruba are not those of Natalee Holloway, who vanished 12 years ago while on a graduation trip with her Mountain Brook classmates.

Her father, Dave Holloway, and private investigator T.J. Ward in August said an 18-month investigation led them to bone fragments that were undergoing DNA testing to determine if they belonged to Natalee Holloway. Tests on the fragments came back negative for a possible match to Holloway, forensic scientist Jason Kolowski told the Oxygen cable network, NBC's Today reported on Tuesday.

The DNA bone sample was ruled out as Holloway after it failed to match to her mother, Kolowski said.

"Out of the four individual bone samples only one was found to be human," said Kolowski, who led the testing and interpretation of the results for the six-part Oxygen series, "The Disappearance of Natalee Holloway," that aired in August.

Dave Holloway and Ward in August 19 launched a new series on the Oxygen network called, "The Disappearance of Natalee Holloway." The showed documented Dave Holloway's journey for justice and described the discovered bone fragments his most credible lead in over 12 years.

Natalie Holloway disappeared May 30, 2005 while in Aruba with 130-plus of her graduated classmates.

For several days during that 2005 graduation trip, the teens - of legal drinking age in Aruba - sunned and snorkeled during the day, and at night donned their sundresses for dinner and partying at Carlos' N Charlie's, which at the time was located in downtown Oranjestad, a decent cab ride from the high-rise district. The group often ended up at Excelsior Casino, which was, and still is, connected to the Holiday Inn where the Mountain Brook group stayed.

On their last night, Natalee and her friends met Joran van der Sloot, who lived with his family in the nearby Montana neighborhood and attended the Aruba International School. She was last seen about 1 a.m. getting into a gray Honda with van der Sloot and the Kalpoe brothers as they left Carlo 'N Charlie's.

Natalee was scheduled to fly home on May 30 but failed to show up when the group met in the lobby to leave for their flight. Van der Sloot and Surinamese brothers Deepak and Satish Kalpoe, reportedly the last people to see Natalee alive, were arrested multiple times in her disappearance, but were always released without being charged. The Kalpoes continue to live and work in Aruba. Van der Sloot is serving a 28-year sentence in Stephanie Flores' death. He also faces charges in Alabama for extorting $25,000 from Holloway.

Both of Natalee's parents have continued their hard-fought battle for justice in the disappearance of their daughter, who in 2011 was declared dead by a Jefferson County judge. Just three months ago, Beth Holloway, as well as television news personality Nancy Grace, appeared on ABC's Dr. Oz show where Holloway talked about "her personal health struggle and never-ending battle for justice."

In 2015, Dave Holloway returned to Aruba yet another time, chasing a lead after a man named Jurrien De Jong told Holloway and Inside Edition that he saw Joran van der Sloot chase her into a small building under construction. De Jong said he never went to the police because he was involved in illegal activities at the time. He says he has come forward now because of a recent TV report where van der Sloot claims he was part of an undercover operation in which Holloway was buried at sea. Prosecutors in Aruba have dismissed De Jong's claims, saying his claims couldn't be true because the building to which he referred had not been built at that time.

Even before his trek back to Aruba that time, along with private investigator TJ Ward and a cadaver dog, Holloway said he was reluctant to get up his hopes. "I don't know how many times I've buried Natalee,'' he told AL.com, "and I don't want to go through that again."

He said then that in his heart, he thinks he knows what happened. He is certain van der Sloot paid a bartender in Aruba to drug Natalee with GHB. He is sure van der Sloot took her home, killed her and, with the help of his influential father, hired South American drug runners to remove Natalee's body from the island, because "they couldn't afford to find a body on the island."

On the Today show in August, Dave Holloway said an informant known as "Gabriel" put Ward and Holloway in contact with a man they claim had direct knowledge of Natalee's disappearance. "We have a person who states he was directly involved with Joran van der Sloot in disposing of Natalee's remains,'' Holloway said. "I thought, you know, there may be something to this."

The scientist told Today that they still don't know if the remains belong to a male or female.