Authorities searching for the killer of North Carolina teen Phylicia Barnes obtained search warrants for email and Facebook accounts belonging to her and at least three other people, according to documents filed in U.S. District Court.

The documents, filed by an FBI special agent assigned to the state's child exploitation task force, say authorities are seeking access to the accounts as part of a child pornography investigation and sexual exploitation of a minor, though the affidavits that spell out that angle remain sealed and agencies involved in the case refused to comment.

Legal experts say the move does not necessarily mean that the case has a sex crime element, but that evidence of sexually explicit material discovered during the investigation is being used as an entry into computer accounts that could provide new insight into her death. Barnes was 16 years old at the time of her disappearance.

"They're likely using that to hammer some people on the [the potential of sexually explicit material] and will use that to hammer back and find out how she died," said Harold Copus, a retired FBI agent who is not involved in the case.

The warrants seek access to two Yahoo email accounts and one AOL email account that include Barnes' first name, along with her Facebook page, records show. The court filings show for the first time some of the secretive tactics being employed by investigators, who have been tight-lipped about the case and publicly have said they have few leads.

In the May 10 federal court filing, unsealed on June 30, FBI Special Agent Jacqueline Dougher, who works from the Baltimore field office with the state's child exploitation task force, also requested access to three other Facebook pages and four other email accounts that appear to be associated with Baltimore men. At least one is linked to a man with the same name as a man previously interviewed by police.

Police have interviewed and reinterviewed those who were among the last to see Barnes alive, and the targets of the search warrant indicate that police are not through with those people. Their identities could not be confirmed, however, and emails sent by The Baltimore Sun to the accounts listed in the search warrant were not returned.

The documents say that authorities "have reason to believe that" within the accounts there is evidence related to a violation of "sexual exploitation of children" and "distribution and possession of child pornography."

The U.S. attorney's office for Maryland, the FBI, and state and city police declined to comment.

"It would be inappropriate at this point to discuss the criminal investigation or do anything that could jeopardize the case down the road," said Greg Shipley, a state police spokesman.

Russell Barnes, the girl's father, said authorities contacted him Wednesday night to inform him that the documents had been made public. But he said officials did not offer any insight into how child pornography relates to the case.

"They said some people weren't being truthful, and they had to go get some search warrants," he said. "They've got it wide open to see what happened."

Barnes, who was from Monroe, N.C., went missing in late December while visiting her older sisters in Northwest Baltimore. She planned to go to college here after graduating early from high school, where she was an honors student and ran track. Authorities said she vanished without a trace, until her nude body was found floating in the Susquehanna River in April.

Maryland State Police and city police are jointly investigating, and the FBI has provided assistance since the early stages. Authorities have not disclosed how she died.

Authorities must have probable cause to obtain the search warrants based on the sexual exploitation and child pornography statutes.

"It's ordinary practice for law enforcement to get search warrants on everybody and anybody who's related to it to see if there's other evidence of other crimes," said Andrew Alperstein, a Baltimore defense attorney who is not involved in the case. But, he said, "a tip is not enough for a judge to issue a search warrant — there has to be reliability to it and probable cause that a crime occurred."

"This is a very high-profile case, and I'm sure law enforcement is using every tool available to them," Alperstein said.

Copus, the retired FBI agent, believes the new search warrants, along with the fact that Barnes' body was found nude, suggests that there is a sex crime element to her death.

"Her being nude will tie back to that eventually," Copus said.

But for now, he said, investigators are casting a "wide net."

"They've got three or four names there that may have communicated with that girl, and they're casting a wide net, trying to find out if they have something else," Copus said.

justin.fenton@baltsun.com

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