A wrongful death trial to decide if a Sonoma County sheriff’s deputy was negligent in the 2013 fatal shooting of a 13-year-old Santa Rosa boy could be delayed by more than a year by the county’s latest legal action.

The county is challenging a January ruling by U.S. District Court Judge Phyllis J. Hamilton that effectively allowed the case brought by the parents of Andy Lopez to go forward. Trial was expected to begin in April.

But attorneys said in legal papers filed in the 9th Circuit Court of Appeals that Hamilton erred in not dismissing all of the allegations against Deputy Erick Gelhaus.

Hamilton dismissed three of five claims that the 27-year veteran violated Lopez’s civil rights but said she would leave it to a jury to decide whether Gelhaus acted unreasonably. Lopez was shot and killed in October 2013 as he walked down the street carrying an airsoft gun designed to resemble an AK-47 assault rifle. Gelhaus told investigators he mistook the gun Lopez was carrying for the real thing.

If appellate justices reverse Hamilton’s ruling, the case would be stripped of its last federal claim and kicked down to state court to try the remaining negligence allegation. The potential for monetary damages would be reduced because the family could not collect attorney fees.

A decision on the appeal could take a year or more.

Lopez family attorney Arnoldo Casillas accused the county of stalling.

“It’s a shame,” Casillas said. “Deputy Gelhaus and Sonoma County are afraid to try this case.”

He said the delay would cost the county hundreds of thousands of dollars in additional fees on top of “a huge verdict” he expected. Casillas settled a Los Angeles County case in which a teenager was shot and injured while carrying a pellet gun for $15 million.

But the county’s attorney, Steven Mitchell, said he believes a jury would find Gelhaus acted legally given the similarity between Lopez’s airsoft BB gun and a real assault rifle.

Mitchell said the appeal is in reaction to an excessive force claim under the Fourth Amendment. He said police and other county agents are immune from such claims unless it can be shown that similar conduct in other cases violated rights. But the family offered no evidence of that, he said.

He commended the judge for striking three other claims, including that Gelhaus was poorly trained or that the Sheriff’s Office provided inadequate training.

Mitchell blamed the family’s decision to pursue constitutional claims in federal court for any delay.

“They made that choice,” Mitchell said. “If they filed a strict negligence claim in state court, this case likely would have been concluded by now.”

Both sides are expected to continue settlement talks. They met in December and followed that with private mediation attempts but could not reach agreement.

Mitchell declined to discuss any sticking points.

“The parties have made efforts to try to get it resolved,” he said. “Thus far, those efforts have been unsuccessful. They will continue to the time of trial.”