Richardson's mother Latice Sutton had pushed for authorities to return to the site where the remains were found, saying there's still a lot of work to be done.
The investigators spent hours combing the area where Richardson's remains were found.
The 24-year-old had gone missing after she was released from the Lost Hills Sheriff's Station in September 2009. She had been arrested for failing to pay her bill at a Malibu restaurant.
Last fall, while at the site mourning Richardson's death, Sutton found one of her daughter's finger bones.
In response to Sutton's concerns about the handling of evidence, Sheriff Lee Baca had told her in December that the FBI had agreed to look into the case.
Eyewitness News has learned that the FBI has declined the request to investigate the handling of the case by the Los Angeles County Sheriff's Department.
Sutton said she is disappointed and frustrated, but she's not giving up.
"My request is for them to examine her body forensically for potential evidence and clues that could perhaps lead us to a suspect because I believe that Mitrice was murdered," she said.
Sutton said there may have been a misunderstanding about what role the FBI should play, so she said she plans to send another letter asking for help from federal authorities to try to figure out what happened to her daughter.
Steve Whitmore of the L.A. County Sheriff's Department said Baca is not deterred and plans to move forward with the investigation.
"We may exhume the remains, we may request the coroner's office to do that, so the remains and the attached clothing can be then forensically analyzed by our crime lab, which, as you know, is one of the best in the nation," he said.
The coroner's office said it does not plan any more searches, but the investigation remains ongoing.