Investigators searching for the killers of two young girls gunned down more than a week ago made a plea Monday for the person of interest named in the case to come forward.

"He must come forward," Jessica Brown, a spokeswoman for the Oklahoma Bureau of Investigation said Monday. "It's his duty as a citizen to come forward and give us information."

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The man, a 6-foot American Indian approximately 35 years of age, is wanted for questioning in connection with the June 8 murders of Taylor Paschal-Placker, 13, and Skyla Whitaker, 11, along County Line Road in Weleetka, Okla. Several witnesses saw him standing by a pickup truck near the crime scene minutes before the shootings.

Brown said the man, who has a "very long ponytail," is just wanted for questioning as a possible witness at this point.

"If we can get a hold of him, we ask him a number of questions and hopefully narrow down the timeline and even possibly get a suspect out of this," she said.

Authorities have interviewed more than 100 people and received around 400 leads in the case, but they are still no closer to finding a motive or suspect in the brutal murders of the young best friends 8 days ago.

Over the weekend, a team lead by the Okfuskee County sheriff's office set up a roadblock near the crime scene and interviewed about 90 people about the case.

"I think we were up close and personal with a lot of people in that particular area of the county," Sheriff Jack Choate said.

Investigators said they are working around the clock to check timelines, perform criminal background checks, re-interview witnesses and family members, and track down leads.

"Community interest, I think, is going to be a big factor in this," Choate said. "It's amazing at what you can find out visiting with local folks in that area, and a lot of them are extremely frightened, you know. They worry about what could happen to their kids or grandkids or any family member, you know, as far as that goes."

On Monday, officials said they would not release a 911 tape made after the girls' bodies were found, saying it wouldn't help advance the case.

Bullets of two different calibers were used to kill both girls, police said, leading investigators to think that possibly two or more shooters were involved.

A reward for information leading to the arrest and conviction of those responsible has grown to more than $30,000, with a third of that money coming from public donations.

"We know someone has information out there," Brown said. "Whether or not they're scared or why they're not coming forward, we do not know. But they do not have to be worried because if we can get the people off the streets who did this, there's nothing to worry about at that point in time, and we need to get this resolved as quickly as possible."

Officials will continue to operate a command center in Okemah, Okla., until the killer is found.

"It is a solveable case," Brown reiterated to FOX News on Monday.