The lawsuit claims sheriff's deputies were negligent, and that they should have known that Mitrice Richardson was mentally ill and had some problems, that they should not have turned her loose after midnight with no identification, no car keys, no phone and no cash.
Richardson was released from the Lost Hills station after midnight on September 17, 2009.
According to family members who have seen it, a videotape taken inside the booking cell shows her clutching the cell's screen, rocking from side to side, lying in a fetal position and unsuccessfully trying to make phone calls.
"I'll make the statement that it did appear to be consistent with somebody who was having some type of mental health crisis," said clinical psychologist Dr. Ronda Hampton.
Richardson was interning with Hampton.
Hampton, Richardson's mother Latice Sutton, and Sutton's attorneys are suing Los Angeles County. They name nine deputies and a commanding officer at the Lost Hills station as defendants. Among other charges: the deputies didn't follow the law and hold Richardson to evaluate her physical and mental well-being.
"The L.A. County Sheriff's Department was grossly negligent, and the officers on that shift, grossly negligent in allowing her to leave and walk out without any form of communication with her family or friends," said attorney Leo J. Terrell.
Deputies on that day were called to Geoffrey's Malibu restaurant. Mitrice Richardson was supposedly acting and talking strangely -- "crazy," said one witness.
Richardson didn't pay her bill, but she did pass a field sobriety test.
She disappeared after she left the sheriff's station.
The lawsuit charges the county with wrongful death. Yet Richardson's mother hopes she's still alive.
"I do have to face the possibility that based on how long she has been missing, she is either being held and transported from place to place, or she may be dead," said Sutton.
Richardson's disappearance prompted the largest missing-persons search in Los Angeles County history.
L.A. County Sheriff's Dept. Spokesman Steve Whitmore said the department is still intent on finding Richardson.
"When a lawsuit is filed, the whole story is not being told, and it will be told," said Whitmore.
Mitrice would be 25 years old in April.
The lawsuit gives the family some leverage it didn't have, access to records they wouldn't otherwise get. They can now talk to deputies under oath.