BOONE CO., Mo. -

According to court documents, local FBI agent, Scott Armstrong, is accused of strangling a teen until he lost consciousness on March 1, 2014. Armstrong was just recently charged with third-degree assault for the incident.

Armstrong is also a part-time employee of the Boone County Cyber Crimes Task Force.

Sheriff Dwayne Carey said, "I found out when a friend called me around 8 this morning from Callaway County."

"I was never notified by the FBI, and so once we talked through all of that, which I was a little bit displeased, we have put the individual on a leave of absence from our task force until the end of this investigation," said Carey.

Court documents state Armstrong strangled the teen using a choke hold, cutting off his air to the point of passing out. They also claim Armstrong admitted putting his arms around the teens neck until he lost consciousness.

Photos were taken of his neck afterward, showing redness that resembled a fabric pattern and a horizontal red mark on the back of his neck.

Carey said, "This is not a Boone County Sheriff's Department employee.  It is an FBI agent and the FBI is investigating this."

It is still unclear how the incident led to the assault.

Armstrong is set to appear in court in Fulton on Tuesday.