Concord police presented their case against 37-year-old Richard Hastings to the district attorney's office in Martinez on Thursday, but prosecutors referred the case back to police "for additional investigation," Senior Deputy District Attorney Nancy Georgiou said.
Police arrested Hastings in Concord on Aug. 21 after launching an investigation earlier this month between the officer and a 15-year-old, according to police.
During the investigation, detectives developed sufficient information to arrest Hastings on suspicion of lewd and lascivious acts with a child, sodomy with a child under 16 years old and contributing to the delinquency of a minor, police said.
He was taken to jail and was later released on bail.
Harry Stern, Hastings' attorney, could not immediately be reached for comment.
San Francisco police spokesman Officer Albie Esparza said Hastings was immediately placed on unpaid leave after his arrest and that the Police Department will conduct an internal investigation.
Hastings is also named in a federal civil rights lawsuit brought by the mother of Washington state parolee Kenneth Harding, who allegedly accidentally shot himself during a 2011 shootout with Hastings and another police officer in San Francisco.
Police said Harding, 19, fatally shot himself as he ran from officers who attempted to stop him in San Francisco's Bayview District on July 16, 2011, after he allegedly failed to pay his bus fare.
According to police, the officers and Harding exchanged gunfire, but when Harding attempted to open fire on Hastings and Officer Matthew Lopez, he instead shot himself.
Harding had been on parole in Washington after serving time for pimping a 14-year-old girl, according to police.