It's been over two weeks since the body of a San Francisco mom was discovered in an area park, and a search began for her missing toddler. But though police have seized tens of thousands of pieces of evidence in the case, they said yesterday that they are still struggling to find the child or track down the killer.

As previously reported, Nicole Fitts, a 32-year-old mother of two who worked at the Harrison Street Best Buy, was found dead on April 8. In a press conference Thursday, police and the FBI gave more details of her slaying, saying that she was "buried in a small, shallow grave" that was discovered by San Francisco Recreation and Parks workers in McLaren Park.

Declining to give her cause of death, San Francisco Police Commander Greg McEachern said that Fitts was "manipulated to fit into the grave," at Thursday's presser. She was buried beneath "a plywood board with odd spray-painted markings," reports the Associated Press.

Saying that police do not believe that the board came from the park, McEachern said that "The plywood has markings on it we hope someone will recognize."

"It is our belief that the person brought the board with them."

At 9:45 on April 1, Fitts was seen on the T-Third in her "blue Best Buy shirt with her nametag." There are no reported sightings of her after that, and she was reported missing on April 5. At that time, her family told police that her 2-year-old, Arianna, was also missing.

Family members say they last saw Arianna in mid-February, and assumed that she was staying with friends or babysitters. According to the AP, Arianna "often spent the night outside of Fitts’ home and she was not in Fitts’ care when she disappeared," McEachern said, declining to elaborate on the child’s custody status.

Though police have interviewed numerous people and "executed search warrants and seized more than 30,000 pieces of evidence at locations in Oakland, Emeryville and Daly City in connection with the locations where Arianna was thought to have been staying," the child's whereabouts remain unknown, McEachern says.

Fitts' co-workers at Best Buy say that Nicole had never mentioned any threats directed at her, and described her as "energetic" and "bubbly."

McEachern says that "police are working on the assumption that Arianna is still alive," and are hopeful that a sharp-eyed member of the public will provide them with the information they need to find her. “Somebody out there knows where she is, somebody out there has information on her whereabouts,” McEachern said.

“We are pleading with you, contact us. Please help bring home that beautiful 2.5 year old girl.”

The SFPD asks that if you see Arianna, call 911 immediately. If you have information on her whereabouts or on her mother's slaying, please contact the SFPD Homicide Unit at 415-553-1145, the SFPD Anonymous Tip Line at 415-575-4444, or text a tip to TIP 411 with SFPD at the beginning of the message.

Previously: SFPD Seeking Missing Two-Year-Old Girl Whose Mother Was Murdered