WELEETKA, Okla. -- Investigators talked with a witness who said he saw two girls moments before they were killed along a county road in east-central Oklahoma, a state agent said.

Oklahoma State Bureau of Investigation lead agent Ben Rosser said they tested the witness' story and believe him to be credible, KOCO-TV in Oklahoma City reported. At a Thursday news conference, Rosser said that the witness offered no names of people he might have seen in the area moments before Taylor Dawn Paschal-Placker, 13, of Weleetka, and Skyla Jade Whitaker, 11, of Henryetta, were shot to death.

Rosser added that he would rather not say whether the witness offered descriptions of people in the area.

State authorities determined Wednesday that two guns were used to kill the girls Sunday along a county road in Okfuskee County, and an OSBI agent added that he believes they're looking for multiple gunmen. However, Rosser said Thursday that he's still open-minded about the possibility of one shooter.

He said tests determined that each girl was shot with both guns. Rosser said he did not want to reveal what caliber bullet killed them. Authorities are still awaiting DNA samples to be returned by a state chemist.

Rosser said detectives still have no suspects in the girls' deaths but that investigators were back at the scene early Thursday. He said an aviation unit with the Oklahoma Highway Patrol was also helping to scour the scene for clues.

The reward for information leading to an arrest and conviction of whoever killed the girls has climbed above $25,000, Rosser said. However, as of Thursday afternoon, he didn't have an exact dollar amount.

During a Wednesday news conference in Okemah, Rosser said authorities have gotten tips and leads from people across the country -- even from a caller in Great Britain. Rosser said 10 agents are working full time on the case and that two agents are gathering intelligence for background purposes.

Rosser said investigators have interviewed several people and that DNA is being gathered from the girls to match up against evidence from possible suspects. Among the worst-case scenarios investigators are considering are that the shooting was random, or the girls stumbled upon something or were targeted. He said Wednesday that he believes the girls were killed where they were found along the road, not killed somewhere else and transported there.

The Okfuskee County Sheriff's Department said the girls had gone for a walk along a bridge during a sleepover. The grandfather of one of the girls went to get them and discovered the bodies, officials said.

"I can't describe coming up on it," Peter Placker said, sobbing uncontrollably as he recalled walking up to the scene, only about one-quarter mile from his house. "I done it once, and I can't do it again."

Meanwhile, relatives tried to make sense of the grisly killings in a community where some residents still leave their keys in their cars and residents who live 10 miles apart still call themselves neighbors.

Skyla was a carefree adventurer, a girl who walked barefoot almost everywhere and rode her bicycle down endless dirt roads. Where she went, her many cats followed, along with her pet goat. Skyla wanted to become a veterinarian, said her grandmother, Claudia Farrow.

Relatives said to know Taylor was to love her. She was the big-hearted girl who rescued helpless turtles crawling in the middle of the road and wanted to become a forensic scientist, like on TV shows, said Placker, who said he raised Taylor as his daughter even though he was her grandfather.

She was home-schooled until the family moved to Weleetka, located about 70 miles south of Tulsa.

"She was the best kid I've known," Placker said.

Funeral services for Taylor will be held at 10 a.m. Friday in Dewar. Skyla will be remembered at 2 p.m. Friday in Henryetta.