(CNN) -- William Whitaker is certain that somebody in the central Oklahoman community where he lives knows who killed his daughter.



Taylor Paschal-Placker, left, and Skyla Jade Whitaker were found shot to death along an Oklahoma road a year ago.



The dirt road where the bodies of 11-year-old Skyla Jade Whitaker and Taylor Paschal-Placker, 13, were found is too remote for the killings to be the work of a stranger passing through, he says.



"There's absolutely no way that somebody from out of the area could've just stumbled upon the place," Whitaker said. "I know whoever did it told somebody, whether they were drinking or bragging or whatever, and whoever knows just needs to bring the information forward."



It has been a year since the two friends were shot multiple times in the stomach and chest less than a half a mile from Taylor's home in the rural community of Weleetka, with a population just over 1,000.



"Taylor was shot five times. My daughter was shot eight times. Thirteen shots between two little girls who never did anything to anyone," Whitaker said. "I don't know how a person can go to work, eat or sleep knowing what they did. I couldn't live with that on my conscience, but they've been doing it for a year now."  Watch father plead for answers in killings »



In the beginning, hundreds of tips poured in. Authorities pursued leads and analyzed evidence, but a year later, they have no suspects or witnesses leading them to any viable conclusions.



Oklahoma State Bureau of Investigation spokesperson Jessica Brown said during a press conference Monday that authorities have "good evidence" in the case but lack the final piece to make an arrest.



"If we could get this one piece of evidence that would help solve this case, that's what we need," Brown said Monday.



Investigators believe that the killer or killers could be from Okfuskee County, or that a member of the community knows something about what happened to the girls the afternoon of June 4, 2008.



"What we are frustrated about is the lack of cooperation we're getting from members of the public," Brown said. She stressed Monday that a $36,000 reward is being offered for information that leads to a conviction.



The girls were shot with two different guns, leading to the possibility that two people were involved, Brown said. The OSBI released a sketch of a person wanted for questioning last year, but they have not received information leading to him, she said.



But the killings remain fresh in the minds of Oklahomans. A billboard with the girls' faces and a tip hotline has loomed over Interstate 40 for several months.



A memorial service was planned for Monday in Weleetka to mark the anniversary.



"I can't go to the dry cleaners, the gym without people asking me, 'what's going on with those two girls?' Everyone in Oklahoma is emotionally involved in this case, and I think it's because it happened to two small children in an area you wouldn't think you'd ever have to worry about," Brown said.



The same posters adorn storefronts and bulletin boards in banks, restaurants and post offices throughout Okfuskee County, a sparsely populated manufacturing region best known as the birthplace of songwriter Woody Guthrie.



Weleetka Police Officer Stacey Rice will never forget the image of the dead girls. He was the second officer on the scene after a relative called 911 around 5:30 p.m. that day.



"I really hope I never see anything like that again. It's just emotionally and visually traumatic. You see two small children lying on the ground like that and it's kind of hard to explain. Makes you want to go find your children," said Rice, a father of two teenage boys.



"It took me several minutes to realize what happened, but after a while, it kind of sank in, and that's when emotions started running ... anger, lots of anger, sadness, disbelief. Nobody wanted to believe what
what is on the billboards? What is the age of Whitaker? did they find who killed them? Who were fatally shot on a rural road?
with the girls' faces and a tip hotline 11-year-old no Taylor Paschal-Placker,
question: what is on the billboards?, answer: with the girls' faces and a tip hotline | question: What is the age of Whitaker?, answer: 11-year-old | question: did they find who killed them?, answer: no | question: Who were fatally shot on a rural road?, answer: Taylor Paschal-Placker,