(CNN) - A conservative activist who made controversial undercover videos of the liberal community organizing group ACORN was one of four men charged Tuesday with attempting to illegally access and manipulate the phone system in a district office of U.S. Sen. Mary Landrieu of Louisiana.
Joseph Basel, 24, Robert Flanagan, 24, James O'Keefe, 25, and Stan Dai, 24, were charged with entering Landrieu's New Orleans office - which is federal property - under "false pretenses for the purpose of committing a felony," according to a news release from the local U.S. attorney's office.
The four posted a $10,000 unsecured bond and were released, said Kathy English of the Department of Justice. According to CNN affiliate WWL, the next court date in the case was set for Feb. 12.
O'Keefe is the same conservative activist who dressed up as a pimp last summer and visited ACORN offices to solicit advice on setting up a brothel, among other scenarios, law enforcement officials confirmed. He secretly
recorded the visits on videotapes that were posted on the Internet, leading to a media firestorm.
Flanagan is the son of William Flanagan, the acting U.S. attorney for the Western District of Louisiana, his office said.
Articles on conservative Web sites connect O'Keefe to a man named Joe Basel, describing them as conservative student activists and filmmakers.
"This is a very unusual situation and somewhat unsettling for me and my staff," Landrieu said in a statement Tuesday night. "The individuals responsible have been charged with entering federal property under false pretenses for the purposes of committing a felony. I am as interested as everyone else about their motives and purpose, which I hope will become clear as the investigation moves forward."
Updated: 8:03 p.m.