In charging documents filed in King County Superior Court, prosecutors asked that bail for Justin Jasper, 22, be maintained at $2 million, citing what they called "the likelihood the defendant will commit a violent offense."
"Although the defendant does not appear to have any criminal history, the state believes he poses an extreme risk to community safety if released," Deputy Prosecutor Daniel Carew wrote.
When Jasper was arrested in the stolen truck, he was in possession of six homemade firebombs, a double-barreled shotgun, a long rifle with a scope, body armor and multiple knives, Carew said in court papers.
Authorities say Jasper also had maps to three Seattle campuses and a recording in which he said he planned to do something in the West to support protesters demanding reform in Brazil.
Arraignment is set for July 22. It was not known Tuesday evening whether Jasper had yet been appointed a public defender.
Prosecutors also asked that Jasper be prohibited from any contact with Erik Henderson, a truck driver in Butte, Mont., who had let Jasper stay at his home.
Henderson told authorities he returned from a trip last week to find his pickup truck missing, and knives and two guns taken from his home. He told The Seattle Times the body armor was his from his days as a contract convoy trucker in Iraq.
The trucker said Jasper described himself as an "anarchist" and had concerns about topics ranging from the chemical industry to genetically altered foods to voting rights, The Times reported.
Computer flash drives recovered from the truck yielded videos in which Jasper introduces himself as "A-Political, atheist and a bastard" and asks, "How many people are supporting in one way or another, the Brazilian revolution? That's what I want to know," according to a probable cause statement filed with the charges.
The statement said Jasper did not state his location but said "that he is local somewhere in the western side of the United States, making sure people understand and notice it."
More than 1 million demonstrators have taken to the streets in Brazil over the past month to denounce everything from poor public services to the billions of dollars spent preparing for next year's World Cup soccer tournament and the 2016 Olympics in Brazil.
Also on the videos, Jasper burns $1 and $5 bills in support of Independence Day and talks about Syria and Brazil and how people should not listen to outside governments, the statement said.
When stopped by University of Washington police who had been briefed about the stolen truck, Jasper told the officers the truck belonged to Henderson and he had permission to use it. He also said he was in Seattle searching for an old friend.
Henderson later told UW police he did not want Jasper driving his truck because the trucker was worried his insurance would not cover any accident.
After being told he was under arrest for investigation of possessing explosive devices, Jasper declined to say anything else to UW officers, their statement said.
Authorities also found maps in the truck to the University of Washington, Seattle University and South Seattle Community College. Court documents identified Jasper's occupation as a self-employed journalist.