A forensic scientist looking into the presumed death of Natalee Holloway said that biological material are required for DNA comparison to confirm the remains found in Aruba belonged to the missing teenager. 

Natalee, 18, of Mountain Brook, Alabama, was last seen during her vacation in Aruba, a Dutch Carribean island off Venezuela.

Natalee’s father, Dave Holloway, conducted an 18-month private investigation that uncovered human skeletal remains at an undisclosed location in Aruba.

Dr. Jason Kolowski said on the fourth episode of the six-part Oxygen series "The Disappearance of Natalee Holloway" Saturday that there’s reason to believe that human remains allegedly dug up in the case match the timeline of the teenager's presumed death in 2005.

“The lead is interesting, but it’s one part of a lot of other things that still have to fall into place to really give this investigation the legs on which to then move forward in handing this over to the Aruban police,” Kolowski says on the episode.

Earlier, the series revealed that skeletal remains of Natalee were mixed with a dog's in an effort to make it difficult for anyone trying to seek the origin of the remains. 

Dutch man Joran Van der Sloot, who is the prime suspect in the case, allegedly paid a man $1,500 to dig up Natalee’s remains.

“You’re really questioning right now the forensic value of what may be left behind,” Kolowski told Dave's private investigator T.J. Ward.

“From what I can tell you, based on everything that is described as far as the disinterment of the remains in 2010, [it] fits with what we would expect for the normal decomposition of the human body, especially in this type of an environment and this type of a locale,” Kolowski said.

To Ward’s investigative team, he added: “The $100 question that you’re not asking is, is that material biologically active and can we use it to identify Natalee?”

“That’s kind of where the problem comes in,” he says on the episode. “It’s decomp material. It’s not exactly blood. It’s not exactly bone or hair or anything like that. Should we find bone, hair even soft tissue still in that gravesite, that’s your biological material. That’s what we want for the DNA comparison.”

After Natalee's disappearance, the Holloways felt unsatisfied with the investigation by Aruban authorities and decided to continue the search for the truth themselves. During the private investigation, skeletal remains were unearthed. An initial test found the human remains belonged to a single person of Caucasian and European descent. Natalee was Caucasian and of European descent.

“We’re going to have statistical probability and a confidence level that this is Natalee or not,” Kolowski told the Daily Mail last month. “We’re waiting on the lab to finalize the data, which they will deliver to me and I will try to turn the data around into results which I will then deliver to Dave.”

"The Disappearance of Natalee Holloway" airs on Saturday 9 p.m. EDT on Oxygen.