Butte County prosecutors have collected equipment from several additional towers along the Pacific Gas and Electric Co. power line suspected of starting last year’s deadly Camp Fire, a sign that the county’s criminal investigation into the historic disaster is progressing.

An attorney for PG&E told lawyers representing wildfire victims and others on Monday that the company had “recently assisted” local prosecutors in their collection of parts from four towers along the high-voltage Caribou-Palermo transmission line.

He said the Butte County district attorney’s office wanted to have the Federal Bureau of Investigation test on cross-arm sections and suspension hooks from those towers — which appears to be the same kind of equipment that malfunctioned on another Caribou-Palermo tower right at the origin point of the Camp Fire.

PG&E has admitted the state probably will find it responsible for the inferno, California’s deadliest and most destructive wildfire to date. The company’s mounting liabilities from that disaster and 2017 blazes prompted it to file for bankruptcy protection in January.

The evidence collection along additional transmission towers, revealed in a Bankruptcy Court filing on Tuesday, could indicate that local prosecutors are digging into PG&E’s maintenance of the overall line as they consider criminal charges against the utility, said Millbrae lawyer Dario de Ghetaldi.

“There’s a lot of possibilities, but one of them is that they identified other components that were about to or likely to fail,” de Ghetaldi said. “They knew that there were problems with that line before the fire. They knew there were problems with that component before the fire.”

PG&E is already on probation because of criminal convictions arising from the 2010 San Bruno pipeline explosion. A federal judge recently expanded the probation terms by imposing several new wildfire-prevention requirements on the utility.

De Ghetaldi, whose clients include Camp Fire victims, said in another Bankruptcy Court hearing last week that a Butte County grand jury was investigating potential criminal actions against PG&E.

Butte County District Attorney Michael Ramsey would not confirm or deny the existence of a grand jury. But his office, working with state prosecutors and the California Department of Forestry and Fire Protection, has been conducting a criminal investigation since shortly after the Camp Fire started, Ramsey said.

“It’s plodding along,” he told The Chronicle on Wednesday. “We’re taking it step-by-step. We’re putting a lot of resources into this.”

PG&E spokesman James Noonan said in an email that the cause of the Camp Fire was still under investigation and “any related inquiries should be directed to the appropriate agencies.”

PG&E acknowledged in February that it had turned off the entire 56-mile Caribou-Palermo line after the company found repairs that “required action.”

After learning about the recent transmission line collections from PG&E attorney Kevin Orsini, attorneys for insurance companies with claims against the utility raced to Bankruptcy Court.

The insurers’ lawyers wanted to delay shipment of the evidence to the FBI’s laboratory in Quantico, Va., hoping to inspect the equipment themselves or at least require PG&E to look at it and report back to them. They were concerned that the evidence could be out of their reach — and of people who lost homes in the Camp Fire — for too long.

Orsini had told the attorneys that Butte County wanted the FBI to conduct “partially destructive” testing on the recently collected equipment — in addition to cross arms and suspension hooks from the tower by the Camp Fire origin point that Cal Fire has possessed since November.

Once the equipment was sent to the FBI lab, “it will not be available for any further examination for the foreseeable future,” Orsini said in the email. Butte County offered to let PG&E inspect the equipment on Wednesday and the company planned to do so, Orsini said.

Yet PG&E decided not to accept Butte County’s offer after all in order not to have unequal access to the evidence, one of the company’s lawyers told U.S. Bankruptcy Judge Dennis Montali on Wednesday. Insurers asked Montali to order PG&E to attend the inspection and relay the information back.

Deputy California Attorney General Nicholas Fogg told the judge that any delay could have “cascading effects” on other areas of the complex Camp Fire investigation. The attorney general’s office is partnering with local prosecutors in their investigation, according to Ramsey.

While the insurers promised to move quickly, the state was wary of allowing any intrusion into the criminal investigation, and ultimately Montali was persuaded.

“I can’t take the risk today of disrupting a criminal prosecution,” he said in deciding against the insurers.

Ramsey would not “say one way or the other” whether the transmission tower equipment had already been sent by Wednesday afternoon. He said the investigation and processing of evidence was “confidential at this time.”

J.D. Morris is a San Francisco Chronicle staff writer. Email: jd.morris@sfchronicle.com, Twitter: @thejdmorris