“A lot of information he did give us was easily accessible online,” Mr. Maslauskas Dunn said. “You just had to do a little research.”

Mr. Hendricks said he and other group members did not accept classified information if it was offered by people in the military. Mr. Hendricks, who said he lived in Olympia and repaired printers for a living, said Mr. Towery had drawn his suspicion more than once in the past, including after he posted inaccurate information about a military movement on an activist Web site.

Yet he and Mr. Maslauskas Dunn, who said he worked as a janitor at a lumber mill in Shelton, Wash., said Mr. Towery’s identity was inadvertently discovered after a public records request made with the City of Olympia. The request yielded an e-mail message Mr. Towery had sent to another person with a military address relating to the protesters’ activities.

That led Mr. Hendricks and other group members to try to determine who Mr. Towery was. After they learned it was the man they had known as Mr. Jacob, they discussed it at City Council meeting in Olympia last week and posted the information on a Web site.

Mr. Maslauskas Dunn said that in a meeting last week, Mr. Towery told him and another group member that he was not reporting information to Fort Lewis and that he genuinely wanted to join “the peace movement” but was under pressure to share some information about protesters with local law enforcement authorities. “What he said is that the world isn’t just in black and white, that there are areas of gray and that it’s in those areas of gray that he lives his life,” Mr. Maslauskas Dunn said.

He said Mr. Towery told them that the Army had reassigned him, at least temporarily, and that he was being investigated “for espionage.” Mr. Maslauskas Dunn and Mr. Hendricks said they were skeptical of suggestions that Mr. Towery might have infiltrated the group purely on his own, as a so-called renegade without Army approval.

Stephen Dycus, a professor at Vermont Law School who focuses on national security issues, said the Army was prohibited from conducting law enforcement among civilians except in very rare circumstances, none of which immediately appeared to be relevant to the Fort Lewis case. Mr. Dycus said several statutes and rules also prohibited the Army from conducting covert surveillance of civilian groups for intelligence purposes.