Detectives are "nearing the end" of an investigation into the October shooting death of 13-year-old Andy Lopez by a Sonoma County sheriff's deputy, a Santa Rosa police lieutenant said Thursday.

But exactly when it will be completed and handed over to the District Attorney's Office for possible filing of criminal charges against Deputy Erick Gelhaus remains unclear.

Police Lt. Paul Henry said he wouldn't commit to a timeline because of the nature of the investigation, indicating it includes forensic pathology and state Department of Justice lab reports. Also, he said, new demands have been placed on detectives by two recent homicides.

"What I can tell you is that it's our interest to do a thorough and complete investigation that is going to meet the needs of the District Attorney's Office, the needs of the Sheriff's Office and, of course, the needs of the community," Henry said.

Acting Chief Hank Schreeder said he didn't think there is anything unusual about the amount of time the investigation is taking.

"These investigations are complex. There are all kinds of layers to them. It's in everybody's best interest to have them done really well," he said. "You can't put a time on it. The investigation is done when it's done. However long it takes."

Lopez, a Santa Rosa eighth-grader, was killed by Gelhaus Oct. 22 after the deputy spotted him walking along Moorland Avenue with what he told police investigators looked like an AK-47 assault rifle.

Gelhaus and a partner drove up behind Lopez and yelled for him to stop. Gelhaus said he fired at Lopez when the teenager turned toward him and raised the gun in his direction. The other deputy did not fire.

It turned out to be an airsoft-type BB gun.

Some members of the community have said Gelhaus' actions were appropriate for the circumstances, but critics of the shooting, including Lopez's family, contend the shooting was not justified. Many have said Gelhaus didn't give the youth enough time to understand what was happening. Others have called on District Attorney Jill Ravitch to charge Gelhaus with murder or manslaughter.

Gelhaus is a 24-year veteran of the Sheriff's Office. He returned to desk duty last month after an internal review found he didn't violate department policies.

Under a county protocol to avoid conflicts of interest, Santa Rosa police have been conducting the investigation. In the beginning, it involved nearly the entire investigative division of 20 to 30 detectives and as many as five sergeants, Henry said.

But as the investigation has stretched into its 12th week, fewer detectives have been devoting entire shifts to it, Henry said. And some detectives have been diverted to lead other homicide investigations, he said.

"It does become a balancing act," Henry said.

He didn't release any new information about the case. In the immediate aftermath of the shooting, police held a press conference in which they answered questions and compared the BB gun with a real AK-47 rifle. Police have provided additional updates to the media.

"I think we've put out a substantial amount of information," Henry said.

Ravitch said this week she is aware of the strains multiple homicide cases have put on the <NO1><NO>Santa Rosa Police Department. She said new cases with suspects in custody should take priority.

She has not received any reports or talked to investigators about the Lopez case, she said. When police submit their final report, it will be reviewed by Chief Deputy District Attorney Diana Gomez, who will go over it with a senior investigator and determine if it is complete, Ravitch said.

Gomez could call for additional investigation, either by her own staff or the Police Department, before making a recommendation to Ravitch about whether the shooting was justified or a criminal act.

The timing of that decision also is unclear. The county protocol established by local police chiefs recommends a 90-day period to consider charges, but Ravitch can take longer.

In her 2010 election campaign, Ravitch criticized her predecessor, Stephan Passalacqua, for taking up to 22 months to investigate police shootings and jail deaths.

"I'm not putting a timetable on anything," Ravitch said this week. "You can't put a timetable on thoroughness."

The FBI initially said it would conduct an independent investigation into possible violations of federal law, but later said it was offering its services to Santa Rosa police if needed. FBI spokesman Peter Lee did not return calls to his office Thursday seeking comment.

Protesters of the shooting have expressed doubt about law enforcement's ability to remain impartial or produce a fair investigation. In numerous marches and vigils, they have called for an outside agency to step in. Many are asking the Board of Supervisors to create a civilian review panel for officer-involved shootings.

A county task force will look at that and other recommendations.