A man who lived in Sterling was arrested for destroying evidence related to an FBI investigation into an ISIS supporter. He had been on the FBI's radar for a year and only recently moved to Virginia.

WASHINGTON — Court documents say an FBI raid at a home in Sterling, Virginia, on Friday was related to an investigation of a possible ISIS supporter.

Sean Andrew Duncan, who moved to Sterling in June 2017, was arrested for “knowingly altering, destroying, mutilating and concealing tangible objects … with the intent to impede and obstruct” an FBI investigation.

The documents said that when FBI agents knocked on the front door with their search warrant, Duncan ran out of the back door barefoot with “something clenched in his fist.”

Agents yelled at Duncan to stop, but before he did he threw a plastic bag over their heads. The documents say the bag contained a memory chip from a thumb drive that “had been snapped into pieces and placed in a liquid substance that produced frothy white bubbles.”

The FBI had been investigating Duncan for more than a year.

Duncan and his wife attempted to travel to Turkey in February 2016, but were denied entry and sent back to the U.S. Upon returning, they were interviewed by the FBI.

A relative of Duncan also warned the FBI that they feared he had become radicalized because he had voiced approval of westerners being beheaded in the Middle East.

When the FBI searched Twitter in December, they found an account created in November 2015 that linked to Duncan’s phone. The Twitter account had a handle with an Arabic phrase that roughly translated to “The Islamic State.”

An unnamed co-conspirator told the FBI in July that Duncan told her he was interested in joining ISIS and they would share news articles from an ISIS publication. The co-conspirator also told the FBI that Duncan had shared an article about how to build a homemade bomb from an al-Qaida publication.

An undercover FBI agent also reached out to Duncan in August claiming to be the unnamed co-conspirator.

The agent told Duncan about an individual who was attempting to arrange travel to Libya, but was “asking various vetting questions.” When the agent asked Duncan if he and his wife were asked similar questions before they traveled to Syria, Duncan told the agent he never had to deal with vetting by contacts because he “always had referrals.”

In June 2017, the Allegheny County, Pennsylvania, Police Department searched Duncan’s phone in an unrelated investigation into the death of Duncan’s infant child. During their search, they found numerous internet searches for ISIS-related material, ISIS attacks, weapons, body armor, defense tactics and YouTube videos of Abu Bakr al-Baghdadi, the leader of ISIS.

The court documents say that the Allegheny County police’s search “discovered over 24,000 positive results after searching a list of common counterterrorism terms.”

Duncan is scheduled to appear to in court on Tuesday. If convicted, he could face up to 20 years in prison.

WTOP’s Dick Uliano contributed to this report.