A lawyer in the Oregon standoff case argued Monday that the court should throw out voluminous Facebook data collected from 23 defendants, arguing that prosecutors lacked probable cause to gather private messages.

U.S. Magistrate Judge Paul Papak issued a search and seizure warrant in April for the Facebook accounts belonging to 23 of the defendants charged in the federal conspiracy case stemming from the 41-day armed takeover of the Malheur National Wildlife Refuge.

While there arguably was probable cause to review the defendants' public Facebook postings, "included in this broad sweep were 'private messages' that Facebook users send or receive from other users - the functional equivalent of email messages, '' defense lawyer Per C. Olson argued.

To show the sheer volume of information the FBI received and went through, Olson noted that Jon Ritzheimer produced 28,000 pages of data, Joseph O'Shaughnessy generated 25,000 pages, the Bundy Ranch Facebook account had more than 5,000 pages and Shawna Cox produced just over 5,000 pages.

The government recovered just under 800 pages from David Fry's Facebook account, including about 108 pages of private messages, said Olson, Fry's court-appointed attorney.

To bolster his case, Olson cited last week's 9th U.S. Circuit Court of Appeals ruling that found a subpoena issued for a cache of messages from former Oregon Gov. John Kitzhaber's personal email accounts as part of an influence-peddling probe was "unreasonably overbroad'' and should have been quashed.

"That case makes abundantly clear that email communications are protected by the Fourth Amendment,'' Olson argued on behalf of the 23 defendants. "There's no grounds for this wholesale gathering of information.''

Olson dismissed a government argument that it needed to obtain all the Facebook material to ensure they knew the identity of each account user. There were no mysteries about who was using each account, he said.

Assistant U.S. Attorney Craig Gabriel countered that the government had probable cause to believe that the defendants in the refuge takeover used Facebook to further the alleged conspiracy. Prosecutors narrowly requested the account information from Nov. 1, 2015, through the defendants' arrests about three months later, Gabriel said.

He said the 91-page search warrant affidavit thoroughly detailed how the defendants used their Facebook accounts to plan and prepare for the refuge occupation, communicate with each other, share photographs of them carrying firearms and standing guard at the refuge and to recruit others to the occupation.

The FBI special agent who signed the affidavit wrote that the Facebook accounts may provide crucial evidence of the "who, what, when, where, and how" of the alleged criminal conduct under investigation.

"Defendants were communicating with each other during the conspiracy. ... Defendants were Facebook friends with each other. ... Whether they were private or public communications is a distinction without a difference,'' Gabriel told the court.

Gabriel said the 9th Circuit ruling in Kitzhaber's case doesn't apply to this because it dealt with a subpoena involving emails, not a search warrant of a Facebook account.

Defense lawyers also challenged the government's two-step process of culling the Facebook material.

FBI forensic officers searched through the material for any relevant information to the alleged conspiracy under a "standardless, ad hoc process,'' Olson said.

"The government informs us that the FBI forensic agents conducting this review are working for the prosecution team; They are not walled off like a filter team,'' Olson wrote in his legal motion.

"The review was done by agents involved in the case,'' Olson argued.

Gabriel said the agents followed rules of federal criminal procedure, which allow for the seizure or copying of all the data, followed by a review of what falls within the scope of the warrant.

"The voluminous production by Facebook leading to a small amount of relevant materials is common,'' Gabriel said. "Judge Papak was fully informed of what the FBI intended to do.''

The FBI turned over to each defendant the full Facebook data received by the government and the material deemed relevant to the pending case. The raw Facebook account data is being kept sealed by the FBI in a secure location and won't be accessed without a court order, Gabriel said.

Defense lawyers also argued in court and through written motions that the magistrate judge lacked the authority to grant the search warrant for Facebook material because the social media data is located in California, outside the U.S. District Court of Oregon's jurisdiction.

Assistant U.S. Attorney Geoffrey Barrow said there was nothing unusual about the search warrant signed by Papak. Federal law, he said, allows the court here to have jurisdiction for an offense that involves stored electronic communications housed out of state.

U.S. District Judge Anna J. Brown said she'd take the Facebook account challenges into consideration and issue a written ruling.

Monday's courtroom was full with spectators, with some turned away. Before the proceeding began, defendant Jason Patrick, released from custody last week and appearing in a blue suit jacket with his standby counsel, shouted out to co-defendant Peter Santilli, who was on speaker phone from jail, "How you doing?''

"Who is that?'' Santilli asked.

"This is Jason,'' Patrick shouted back. "Apparently, I'm less dangerous than a radio talk show host.''

"Oh my goodness,'' Santilli responded on the speaker phone.

At 1 p.m. Monday, U.S. District Judge Robert E. Jones is expected to hear Ammon Bundy and his brother, Ryan Bundy, argue for their pretrial release.

They have pleaded not guilty to the federal conspiracy charge and are set to go to trial Sept. 7. They're among 26 defendants who were indicted on the charge of conspiring to impede federal works at the Malheur National Wildlife Refuge.

Seven defendants have pleaded guilty to conspiracy; an eighth defendant is scheduled to plead guilty to the charge Tuesday.

-- Maxine Bernstein

mbernstein@oregonian.com

503-221-8212

@maxoregonian