(CNN) Authorities have arrested an 18-year-old Ohio man who the FBI says threatened to assault federal law enforcement officers in an online post and showed support for mass shootings.

A criminal complaint alleges that Justin Olsen of Boardman, just south of Youngstown, discussed the 1993 Waco siege on iFunny, a mobile app for memes and funny images, in June.

He blamed the Bureau of Alcohol, Tobacco, Firearms and Explosives for the deaths of scores of people living at the site, the complaint filed by an FBI agent says.

"In conclusion, shoot every federal agent on sight," Olsen wrote at the end of the discussion, the complaint says.

The FBI went to Olsen's house last Wednesday, where they found 15 long guns, 10 pistols, about 10,000 rounds of ammunition and camouflage clothes.

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