Federal authorities arrested and charged a Sterling, Va., man with attempting to obstruct a terrorism investigation on Friday, accusing him of acting in a manner that was "indicative of an individual planning and researching how to conduct an attack," according to records filed in federal court.
The filing says Sean Andrew Duncan, who moved to Sterling from Western Pennsylvania in June, had owned a phone that revealed prolific research into materials relating to the Islamic State, terrorist attacks, weapons, surveillance tactics and body armor.
He is to make his initial appearance in court on Tuesday following an arrest on the 46900 block of Courtyard Square that involved his alleged destruction of a computer thumb drive that authorities suspect may have contained evidence of criminal activity.
Neither Duncan nor his relatives could be located for comment. As of Saturday evening, it was unclear whether Duncan had legal representation.
Federal investigators first became aware of Duncan's activities in February 2016, according to a court affidavit submitted by Special Agent Katherine Campo. A relative had reported to the FBI that Duncan had converted to Islam, possibly radicalized, and had begun praising the beheadings of Westerners in the Middle East. Around that time, he and his wife, who is not identified in court records, booked a trip to Istanbul departing from Dulles International Airport, but were denied entry to Turkey and returned to the United States, where federal agents interviewed him, according to the affidavit.
Shortly afterward, Duncan allegedly deleted his Facebook account and changed his cellphone number, which ended in "7730," the same ending authorities believed was also associated with a Twitter account that contained an Arabic phrase that roughly translated to "The Islamic State."
Investigators began building their case based on information provided by an unnamed source referred to as a co-conspirator who was in the custody of a foreign government for trying to join the Islamic State. The filing says the source told investigators Duncan was an American contact who had wanted not only to join the terrorist organization, but also to orchestrate a domestic attack.
Communicating through an encrypted mobile messaging application, the source told investigators that Duncan shared articles from an Islamic State news outlet and said he agreed Muslims should attack their own countries.
Once, according to the affidavit, the source claimed to have criticized non-Muslim women for wearing shorts that expose their bodies. In response, Duncan allegedly told the source to "try this," sending a link to an article published by an al-Qaeda magazine titled, "How to build a bomb in the kitchen of your mom."
Twice, the source said, Duncan had asked her to travel to Syria with him and become his wife, and twice she refused, according to the affidavit.
The case deepened in June. That was around the time when Duncan's infant child died. While investigating what happened – the cause of death in the autopsy report was inconclusive – the Allegheny County (Pa.) Police Department obtained Duncan's phone. A copy of it quickly came under FBI scrutiny. Investigators, according to court records, found hundreds of searches that involved terrorism-related activities between March and June. They included Islamic State-related materials, terrorist attacks, searches for hidden cameras, body-worn cameras, military-style combat gear, bulletproof armor, M-4 rifle magazines, an AR-15 rifle, a YouTube video on how to "reinforce door with a barricade," and the leader of the Islamic State, Abu Bakr al-Baghdadi, the filing states.
On Friday, as federal agents forced their way into his home, Duncan ran out the back door, barefoot, clenching a plastic bag in his fist, according to court records. The clear plastic bag contained a thumb drive that had been broken into pieces and submerged into a frothy, bubbly liquid.
"I believe that the thumb drive was snapped in pieces because Duncan altered, destroyed, and mutilated it in order to impede and obstruct the FBI's investigation of him for attempting to provide material support to terrorists," Campo, the agent, wrote in the affidavit.
The arrest marks the latest in a series of cases made since 2015 against northern Virginia men who authorities have alleged had connections to the Islamic State. Another Sterling man, Mohamed Bailor Jalloh, was arrested in July 2016 and accused of trying to plan a domestic terrorist attack on behalf of the Islamic State.
The Washington Post's Peter Jamison, Rachel Weiner and Julie Tate contributed to this article.