One year after his daughter and her best friend were killed on a dusty Oklahoma road, William Whitaker takes comfort at the makeshift memorial under the tree where the two young girls were found dead.

"It's a very beautiful place down here," he tells FOX 25 in Oklahoma City standing next to dozens of flowers, teddy bears and a cross with a photo of the girls. "I've spent lots of time down here. It's been a rough 12 months."

The double-murder of 13-year-old Taylor Paschal-Placker and 11-year-old Skyla Jade Whitaker a year ago Monday has left a quiet Oklahoma town and a nation in shock.

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The girls were best friends. They were sleeping over at Taylor's house and had decided to take a walk.

They were gunned down near a bridge about a quarter-mile from Taylor's house.

Law enforcement officials pleaded for the public's help Monday in finding the killler or killers.

Oklahoma State Bureau of Investigation spokeswoman Jessica Brown says investigators "are one piece of information" from making an arrest.

Brown said more than 7,500 man hours have been spent trying to solve the killing with more than 450 interviews and tests on more than 700 pieces of evidence.

"I think about the girls and what they liked to do and how they loved to go fishing and be with all their animals and play with them," an emotional Whitaker said.

Law enforcement officials pleaded for the public's help Monday in finding the killler or killers.

"I pray for it to come to an end, and they find the right person...persons that did it," Whitaker told FOX 25. "Justice will be served."

The girls' deaths stunned neighbors and friends in Weleetka, a working-class community of about 1,000 people, located 70 miles south of Tulsa.

Click here to read more on this story from FOX 25 in Oklahoma City.

The Associated Press contributed to this report.