When agents raided the Boardman, Ohio, house where Justin Olsen was living they recovered 15 rifles, 10 semi-automatic pistols and roughly 10,000 rounds of ammunition, according to a criminal complaint written by FBI Special Agent Themistocles Tsarnas and seen by NBC News.
Olsen, who wrote under the name "ArmyOfChrist," was charged Monday with one count of threatening to assault a federal law enforcement officer.
"ArmyOfChrist discussed supporting mass shootings, and assault and/or targeting of Planned Parenthood," according to Tsarnas.
Assistant Mahoning County Prosecutor Michael McBride decided authorities had to act swiftly on the threats in the wake of the recent mass shootings in El Paso, Texas, and Dayton, Ohio, NBC affiliate WFMJ reports.
The case against Olsen began earlier this year when FBI agents in Anchorage, Alaska, working in a chat room called "iFunny," found a user named ArmyOfChrist making threatening comments.
That user wrote online that he supported the Oklahoma City bombing in 1995 and the shootings of ATF agents at the siege of the Branch Davidians compound in Waco, Texas, in 1993.
"Hell even the Oklahoma City bombing shows that armed resistance is a viable method of political change. There is no legal solution," ArmyofChrist wrote on Aug. 6, according to the complaint. "In conclusion, shoot every federal agent on sight."
Agents raided his place of residence, described in the complaint as his father's home, on Aug. 7 and found a large number of guns and bullets throughout the house and in a gun vault in Olsen's room.
Olsen allegedly told agents that his writings were "only a joke."
Olsen also characterized his comments as "a hyperbolic conclusion based on the results of the Waco siege ... where the ATF slaughtered families," according to the complaint.
A message seeking comment was left with Olsen's attorney.
Agents seized 15 rifles, 10 semi-automatic pistols and roughly 10,000 rounds of ammunition during the arrest.
Olsen is still in custody and scheduled to make an appearance in U.S. District Court in Youngstown on Friday.--NBCNEWS