PHOENIX — In a case with statewide implications, the Arizona Supreme Court is being asked to decide whether circumstantial evidence that a candidate knew of forged signatures on petitions is enough to disqualify him from the ballot.

Tim La Sota, attorney for state Sen. Don Shooter, R-Yuma, acknowledged in filings with the high court that there is no hard evidence that Toby Farmer, Shooter’s Republican primary opponent, knew the signatures were forgeries.

But La Sota said there is no other plausible explanation. And he said it should not be necessary for him to prove that.

“Perhaps a witness could be found who could attest to the candidate’s knowledge of the forgery,” he argued to the high court.

“But the candidate who participates in the forging of petition signatures is unlikely to do this in front of people,” La Sota continued. “He is likely to do it when nobody is around who could witness it.”

What the justices decide will most immediately affect whether Shooter, first elected to the Senate in 2010, will have to face off against Farmer in the Aug. 26 Republican primary.

But the ruling also could set a precedent that would affect future ballot fights.

La Sota told the justices that siding with Farmer would essentially be an invitation for candidates to simply submit forged names, since there would be no way to prove they knew the signatures were fake.

At a hearing earlier this month, Maricopa County Superior Court Judge John Rea ruled that it is “clear from the evidence presented” that there were forgeries on petitions Farmer said he circulated, with seven instances in which someone other than the person whose name appears actually signed the paperwork. And Rea also noted that Farmer signed an affidavit avowing the people who signed the petitions did so in his presence.

“However, there has been no evidence that Mr. Farmer knew that the forgeries were occurring,” Rea wrote. There also was testimony that the forged signatures did not match Farmer’s handwriting.

Even after eliminating the forged signatures, Farmer had enough valid names to be on the ballot.

La Sota noted the names on the petitions at issue were in alphabetical order by street address, which he said shows they could not have been collected at some central location. Beyond that, he argued Rea’s ruling is based on the presumption that five different people committed petition forgery without Farmer knowing anything about that.

La Sota argued the fact that the signatures were in alphabetical order shows Farmer had not gone door to door to get the names.

He told the justices that what they decide here will affect future elections.

“If petition forgery on the part of the candidate is not proven under these facts, it is hard to know under what facts, if any, it would be possible to prove petition forgery,” he wrote.