"The charges against the defendant are very serious," said Sharon Ovington, a Magistrate Judge in the Southern District of Ohio.
Several other people suspected of attacking police at the Capitol also appeared in federal courts around the country.
Crowl is a self-employed carpenter in Champaign County, Ohio and a veteran of the Persian Gulf War. Prosecutors said he does not have a stable address. He and his associates Thomas Caldwell and Jessica Watkins are the first suspects to be charged with plotting to take over the US Capitol to stop Congress from certifying Joe Biden's election as US President over former President Donald Trump.
All three are members of the Oath Keepers, a loosely organized anti-government militia.
Crowl's attorney said his client suffers from skin cancer and cannot get proper treatment in jail. He also said that as a war veteran, Crowl could be trusted to abide by any rules of release the judge might impose.
But Ovington said releasing Crowl to a home that apparently contains nine firearms was a "non-starter."
In an amended complaint, investigators said they have uncovered damning messages exchanged between the three suspects showing an apparent coordinated effort to storm the Capitol.
Caldwell, whom prosecutors describe as a leader in the organization, also received messages while he was inside the Capitol from an unidentified person who appeared to direct him down to the building's underground tunnels.
"All members are in the tunnels under capital seal them in. Turn on gas," one message said.
At Crowl's hearing, the government said the FBI had discovered instructions on how to build explosives during the execution of a search warrant at the home of one of Crowl's co-conspirators.
The prosecutor also read aloud excerpts from Internet posts made by Oath Keepers founder Stewart Rhodes, in which he urges his members to essentially prepare for a civil war.
On the group's site, Rhodes wrote that the Biden administration was "an illegitimate regime" headed by a "puppet who will do the bidding of a mortal enemy of this nation." More than 150 people so far have been charged for their role in storming the US Capitol, according to a Reuters tally. The FBI has made arrests daily, as agents comb through more than 200,000 photos and videos in which many suspects are seen pushing past police, ransacking offices and bragging about their actions.
The FBI has linked a number of suspects to fringe groups such as Oath Keepers and Proud Boys, or believers of discredited conspiracy theories such as QAnon.
Also on Friday, a Colorado man the FBI identified as a member of the Three Percenters militia, "loosely allied with the Oath Keepers," appeared in federal court for his suspected role in the attack, court documents showed.
A judge ordered Robert Gieswein, 24, of Woodland Park, Colo., to be held without bond as he faces five charges including assault on a federal officer.
In a federal court in New York, a judge ordered Jeffrey Sabol of Colorado to be detained pending trial. Prosecutors said he dragged a police officer down a set of stairs at the Capitol.
In New Jersey, a local gym owner, Scott Fairlamb, also appeared in court on allegations he punched a police officer in the head at the US Capitol.
His attorney Harley Breite said his client plans to plead not guilty.
Judge James B. Clark III said Fairlamb's participation in the event is a "badge of dishonor," but ruled he could be released on a $50,000 bond. Prosecutor Catherine Murphy said the government would appeal the ruling.
Kevin Strong, a Qanon believer who works for the US Federal Aviation Administration, has also been arrested, charging documents released on Friday show. The FBI said that last week it confiscated two guns, a cellphone and other devices from his home in Beaumont, California.
The documents said Strong sent messages to another individual claiming that "World War 3 is going to occur" on Jan. 6."He had recently purchased a new truck and believed that QAnon would cover the debt," the documents said. He was photographed attending the riots, and later told the FBI during his interview he had "Q clearance."