PORTLAND, Maine — An Auburn man and Lewiston woman arrested New Year’s Eve in Bangor on charges of aggravated sex trafficking have been charged in federal court with transporting a teenager in interstate commerce with the intent that she engage in prostitution and aiding and abetting the same.

Alvin Houston, 27, of Auburn and Shawna Calhoun, 24, of Lewiston are accused of prostituting the girl through advertising pay-for-sex services via the free classifieds website Backpage.com, according to documents filed in federal court in Portland.

They were scheduled to appear Monday afternoon before U.S. Magistrate Judge John H. Rich III.

Both defendants were released Monday from the Penobscot County Jail to members of the U.S. Marshal Service, according to information posted on the court’s electronic case filing system. They had been held at the jail unable to make bail since their arrest Dec. 31 at an Odlin Road motel.

The state sex trafficking charges against Houston and Calhoun have been dismissed, according to Michael Roberts, deputy district attorney for Penobscot County.

“The U.S. attorney’s office has better resources to deal with this case and the defendants, if found guilty, most likely will get more severe sentences [because of the weight the federal sentencing guidelines give to criminal histories],” Roberts said Monday.

Both defendants have criminal histories, he said.

An investigation into the whereabouts of a 13-year-old Lisbon girl who reportedly ran away from home Dec. 21 led to the arrest of Houston and Calhoun, according to court documents.

The girl told investigators that she had “engaged in prostitution” in Portland and Boston, the affidavit filed in federal court in Portland said.

The ad, copies of which were included in the affidavit filed Jan. 2 at the Penobscot Judicial Center, was for a 21-year-old “Spanish Doll” available for outcalls in the Bangor area.

The girl was with the pair when FBI special agents and Bangor police conducted a sting at the hotel on New Year’s Eve, according to a previously published report.

The teenager, who was not arrested or charged, was released to her mother about 5:30 a.m. Jan. 1, according to Bangor police.

If convicted of the federal charges, Calhoun and Houston face up to 10 years in prison and a fine of up to $250,000. They faced the same amount of time on the state charges but a fine of up to $20,000.

BDN writer Dawn Gagnon contributed to this report.