There have been "credible sightings" recently of a California woman who vanished nearly a year ago after being released from a sheriff's station, authorities said Wednesday.

The Las Vegas, Nevada, Police Department will hold a news conference Thursday to update the search for Mitrice Richardson, police said.

"There's been some credible sightings," Steve Whitmore, spokesman for the Los Angeles County Sheriff's Office, told reporters. "It's not definite. We are going to ask the public's help in locating her."

"We want to let her know if she is listening that she is not in trouble and will not be subject to arrest. We just want her to know that it is ok to contact authorities and family, and to let us know that she is alive."

Richardson, who was 24 when she disappeared but would be 25 now, is a former beauty pageant contestant who was last seen leaving a Malibu, California, sheriff's station in the early morning hours of September 17, 2009.

She had been arrested the previous evening at an upscale restaurant after allgedly not paying for her meal. Patrons at the restaurant said Mitrice exhibited strange behavior.

Richardson's family has said the college honors graduate suffered from mental health issues and should have been kept at the sheriff's station until a relative arrived to pick her up.

A court has declared Richardson dead, although no body has been found.

Whitmore said the credible sightings were in the Las Vegas area.

Ronda Hampton, a close friend of Richardson's family, said an acquaintance of Richardson's told police he saw her at a casino last month. Hampton said that after observing her for about three hours, the acquaintance approached the woman who appeared to be Richardson and asked, "Where have you been?"

"The woman turned around and looked as if she didn't know him (the acquaintance) and then looked at him again, then she ran off with some woman," Hampton told reporters.

Latice Sutton, Richardson's mother, told reporters she doesn't consider the sighting credible. "I don't discount that he (the acquaintance) may have seen someone who he believed was Mitrice," Sutton said, "but I don't believe he is absolutely certain it was Mitrice."

At the same time, Sutton was hopeful it could have been her. "I think anything is possible," she said, "and I pray that it is Mitrice."

Last month, Sutton sued the county of Los Angeles and several sheriff's officials for wrongful death and negligence in her daughter's disappearance, according to court documents.

Sutton argued in the lawsuit that the sheriff's department failure to administer psychiatric or medical evaluations and the fact that Richardson was released "alone in an unfamiliar area without money, a cellular phone or means of transportation amounts to negligence." The lawsuit seeks unspecified monetary damages.

Whitmore told reporters in September that the decision to release Richardson was made because "she was not intoxicated, she didn't exhibit any mental issues, so when we were done running her fingerprints and criminal history, then we are obligated by law to release her from custody."

He also has said that a female jailer "offered to her to stay the night. She could have stayed, but she wanted to leave."