CLEVELAND, Ohio — Federal prosecutors on Monday charged a Boardman man with making threats against law enforcement, following an investigation that revealed he voiced his support online of mass shootings and lived in a house with 25 guns and 10,000 rounds of ammunition, records show.

Justin Olsen, 18, faces a charge of threatening to assault a federal law enforcement officer. Authorities arrested him on Aug. 7 on state charges and he was taken to the Mahoning County Jail. He has been in custody ever since

Olsen used the handle “ArmyOfChrist” as his moniker on iFunny, a website where people can posts memes, photos and statements on a variety of topics. There, he told fellow users that he supported mass shootings and attacks on Planned Parenthood, according to an affidavit written by FBI agent Themistocles Tsarnas.

The threats included a June 2 discussion about the Branch Dividians in Waco, Texas, officials say. In 1993, cult leader David Koresh and many of his followers were killed following a standoff and raid by state and federal law enforcement.

Olsen wrote, “in conclusion, shoot every federal agent on sight,” according to the affidavit.

While an investigation into Olsen began in February, a prosecutor in Boardman, 80 miles southeast of Cleveland, said on Aug. 6 he could not wait to act on the information in light of recent mass shootings in the U.S., a Boardman police report said. Authorities arrested Olsen as he walked from his home to his car.

Olsen made his initial appearance Monday in front of a federal magistrate judge in Youngstown. Preliminary and detention hearings are set for Friday.

His attorney Ross Smith did not immediately respond to a message.

Tsarnas’ affidavit says FBI agents in Alaska began investigating “ArmyOfChrist” because of postings that supported violence. By March, the FBI noticed that about 4,400 people subscribed to his account, which showed a large increase over the previous month.

Olsen also posted statements such as “don’t comply with gun laws, stock up on stuff they could ban. In fact, go out of your way to break these laws, they’re f-----g stupid,” the affidavit says. He also wrote “Hell, even the Oklahoma City bombing shows that armed resistance is a viable method of political change. There is no legal solution,” according to the affidavit.

The latter was a reference to Timothy McVeigh, who is responsible for the largest domestic terrorism attack in U.S. history. McVeigh, who was executed in 2001, become something of a cult figure among mass shooters and in dark corners of the internet.

Olsen’s postings appeared “politically motivated,” and he also posted that he was accepted into a ROTC program in Alabama, according to the police report. He also noted that he planned to move to Austin for college after he was accepted to the University of Texas through an ROTC scholarship.

Agents subpoenaed iFunny for the email address associated with “ArmyOfChrist” and traced it back to Olsen, the affidavit says. The case was sent to the FBI’s office in Youngstown in early August.

Olsen admitted to Tsarnas during his arrest that he posted comments about violence on iFunny from his cellphone but said they were “only a joke,” the affidavit says. He said the comments regarding shooting federal agents were “a hyperbolic conclusion based on the results of the Waco siege … where the ATF slaughtered families,” according to the affidavit.

Olsen also said he made the postings on his “s--t account,” the police report states.

When officers went to Olsen’s father’s house on Aug. 7, they saw about 300 rounds of ammunition on the stairway leading to the second floor. They entered the home for a safety sweep, seeing a computer and iPad in Olsen’s room. In another bedroom, they found rifle cases, thousands of rounds of ammunition, camouflage clothing and camouflaged backpacks, along with a large gun vault, the affidavit states.

Inside the vault were AR-15-style rifles and shotguns.

In all, the search of the house resulted in the seizure of 15 rifles, some of which were assault-style, as well as 10 semi-automatic pistols and an estimated 10,000 rounds of ammunition, according to the affidavit. Authorities also found a machete in the trunk of Olsen’s car.

Olsen’s arrest came within the same week Connor Betts opened fire in a popular entertainment district in Dayton, killing nine and injuring dozens of others before police shot and killed him. That shooting, which happened Aug. 4, came less than a day after another man opened fire inside a Walmart in El Paso, Texas, killing 22 and injuring numerous others.

“Urging people to shoot federal agents is never acceptable,” U.S. Attorney Justin Herdman said in a statement. “This defendant had access to an arsenal and we take his threats very seriously.”

This article was updated to include the correct year that Timothy McVeigh was executed.

If you would like to comment on this story, please visit Monday’s crime and courts comments section.