Homeland Security
An employee of the US Department of Homeland Security was found to have a gun, knives and thermal imaging equipment, according to a court filing by federal officials.SAUL LOEB/AFP/Getty Images

Officials have arrested an employee at the US Department of Homeland Security who they believe was plotting to attack the agency.

West Virginia resident Jonathan Wienke was caught in possession of a gun, a knife, pepper spray, thermal imaging equipment and radio "devices" at the agency's Washington headquarters in early June, according to court documents.

Wienke had top-secret clearance inside DHS headquarters, a building that houses 3,000 employees. His office was located in an area of the building close to the site of a planned meeting of high-level officials the day of his arrest, which he was aware of, according to the documents obtained by the local NBC News station.

Authorities have "probable cause to believe" that Wienke was "conspiring with another to commit workplace violence, and more particularly may have been conspiring or planning to commit violence against the senior DHS officials in the building," stated the documents.

Everything but the gun and bullets were found on Wienke, when he was chosen for a random screening upon entering the building on the day of his arrest on 9 June. DHS officials then accompanied Wienke to his office and screened him again, which is when they discovered a loaded gun and five hollow-point bullets, said the court filing.

Wienke has pleaded not guilty to the gun charge against him and is awaiting a court date as officials continue to investigate further charges against him. Meanwhile, the defendant has been placed on administrative leave.