Days after mass shootings in El Paso and Dayton rocked the nation, FBI agents raided the home of an Ohio man who allegedly threatened to commit his own massacre. Inside, they found more than a dozen rifles and 10,000 rounds of ammunition, the FBI said.

Justin Olsen, 18, was arrested Monday for allegedly threatening to assault a federal law enforcement officer. He’s accused of making the threats on a meme website where he also allegedly discussed shooting Planned Parenthood locations, citing multiple mass murders involving far-right extremists.

Olsen allegedly made the threats on iFunny, a meme-sharing site where he used the name “ArmyOfChrist” and a picture of a medieval crusader as his avatar. (The crusades are a popular theme in some far-right Christian circles.) His account had more than 5,000 followers as of Tuesday morning before it was suspended.

Olsen’s arrest comes as federal agencies are facing increased pressure to take action against domestic terror following a series of mass shootings, several of which were connected to ominous posts online.

An FBI office in Anchorage, Alaska flagged the posts, and the bureau continued to monitor them as they grew more specific, FBI spokesperson Vicki Anderson said.

A search of Olsen’s house last Wednesday, where he reportedly lived with his father, turned up a trove of weapons, including 300 rounds of ammunition on a staircase, another 10,000 rounds in a bedroom, 15 rifles including AR-15 style rifles, and 10 semi-automatic pistols, and a machete in Olsen’s car. A search warrant reveals authorities searched Olsen’s property for “hate related literature.”

Olsen allegedly told investigators his posts were “only a joke” and that the reference to shooting agents was “a hyperbolic conclusion based on the results of the Waco siege.”

His lawyer did not immediately return a request for comment.

In chats, Olsen allegedly cited the bloody 1993 confrontation between federal agents and a religious sect in Waco, Texas. The shoot-out resulted from a standoff between Branch Davidians and federal law enforcement, who accused the group of child sex abuse and hoarding illegal weapons. A pair of shooting battles and a 51-day standoff killed 76 Branch Davidians and four federal agents.

In screenshots included in court papers, Olsen allegedly cited Waco as justification to “shoot every federal agent on sight.”

Extremists, including Oklahoma City bomber Timothy McVeigh, have cited Waco as justification for their own violent acts. Olsen allegedly referenced McVeigh as committing “a viable method of political change” when he killed 168 people in a federal building with a truck bomb in 1995. Olsen also allegedly called on followers to “stock up” on illegal firearms.

Anderson said the agency has been receiving more tips about suspicious online activity.

“People are more vigilant right now, so we’re getting more calls, citizens calling in about concerning posts they see,” she said. Often, “people second-guess themselves, but too many times after one of these horrific events occurs, we find out people had concerns.”