Authorities who allege a Las Vegas woman planted a human finger in her Wendy's chili may have a difficult time convicting her of an illegal hoax, experts said Monday.

Wendy's Chili Finger Incident Background: 'Chili Finger' Incident View Images: Customer Claims She Discovered Finger In Chili View Images: Police Search Home in 'Chili Finger' Incident View Images: Leopard Attack New Twist In Finger Incident View Images: Arrest Made In 'Chili Finger' Case Wendy's Responds To Arrest

The evidence made public so far is circumstantial and may not be admitted before a jury, and where the finger came from remains a mystery.

Santa Clara County authorities allege that Anna Ayala, who is scheduled to appear in court in Las Vegas on Tuesday, may have put the finger into the chili she was eating last month in San Jose, as part of a concocted scheme to sue the fast-food chain, just like she's sued other restaurants and employers.

"All they can do is circumstantially establish, from the start to the finish, that somebody lost their finger and it ended up in her chili," criminal defense attorney Daniel Horowitz of Oakland said of the case.

The authorities so far have not identified who the finger belonged to, or Ayala's alleged connection to it. In addition, while San Jose authorities obtained an arrest warrant last week based on the woman's litigious history, there's no guarantee such evidence would be admitted at trial.

"It's not coming in," Horowitz said. "The only reason it would come in was to show a state of mind, and she conceded that she was going to file a complaint. It if did, it would be prejudicial."

Ayala, 39, is accused of attempted grand theft, a charge authorities said relates to the millions in dollars of financial losses Wendy's has suffered since news broke of her claim that she bit a 11/2-inch finger tip in a mouthful of her chili on March 22.

She hired a lawyer and filed a claim against the franchise owner, but dropped the legal fight shortly after police searched her Las Vegas-area home.

Ayala has been involved in nearly a dozen legal battles, including a sexual harassment suit against an employer, an auto dealer over a car and even another fast-food chain for food poisoning.

Michael Markowitz, a former prosecutor and now a Contra Costa County criminal defense attorney, said the admission of Ayala's litigious past could be damaging at trial, especially since there is no evidence publicly known linking her to where the finger came from. A judge might admit her past, he said.

"That would be a large part of the DA's case against her," Markowitz said.

He noted that in the ongoing Michael Jackson sexual molestation case, allegations of past sexual misconduct were introduced. Cases based entirely on circumstantial evidence can be winners for prosecutors, like the Scott Peterson trial, in which Peterson was convicted of killing his pregnant wife without any evidence directly linking him to the murders.

"Jurors are instructed to accept circumstantial evidence if its believable," Markowitz said.

Experts said Ayala's defense is doomed if authorities trace the finger's owner and link Ayala to that person.

A person with knowledge about the case who spoke on condition of anonymity said the finger charge stemmed from San Jose police interviews with people who said Ayala described putting a finger in the chili, statements bolstered by authorities announcing last week that it did not appear the finger had been simmering in chili.

The company maintains that the finger did not enter the food chain in its ingredients. Employees at the San Jose franchise were found to have all their fingers, and no suppliers of Wendy's ingredients reported any hand or finger injuries, the company said.

Ayala, who has maintained her innocence, faces a maximum seven-year sentence if convicted of the finger charges, and at least another 16 months if convicted of unrelated charges that she allegedly bilked a woman $11,000 over a soured deal over a mobile home two years ago.

Ayala is to appear in Las Vegas court Tuesday before being transferred to San Jose to face charges. If Ayala does not fight extradition, she could be whisked within hours or days to San Jose, said Christopher Laurent, the chief Clark County deputy district attorney handling her case.

"I would imagine she will be gone in the next five days," Laurent said Monday.

Frederick Tait Ehler, Ayala's attorney, declined comment. Santa Clara County Assistant District Attorney Karen Sinunu declined comment as well.

Wendy's spokesman Denny Lynch said the chain, based in Dublin, Ohio, is offering $100,000 for information leading to where the missing finger originated. The reward has not been paid, Lynch said.