Barnes entered court with his legs and hands shackled. He wore a brown shirt and blue shorts. He told a judge he did not have the money to afford an attorney and requested one be appointed by the court.
Assistant U.S. Attorney Kurt Erskine said the government will move to keep Barnes in custody.
Barnes previously was indicted by a grand jury in Fulton County on charges connected to alleged vandalism. Mitchell pleaded guilty in January to conspiring to pay more than $1 million in bribes to win city business and has agreed to testify against others.
Contractor Charles P. Richards Jr. pleaded guilty in February on similiar charges in relation to the federal investigation.
In the Barnes incident, dead rats were left on Mitchell's property and brick was thrown through Mitchell's window with the words "Shut Up" and "ER Keep Your Mouth Shut" written on it.
Mitchell told police at the time he was working with federal authorities on a case.
At the time of Barnes' arrest last November, a police report stated he admitted to damaging Mitchell's home. But in June, the Fulton County District Attorney's Office dropped the charges because federal prosecutors wouldn't turn over key evidence in the case, including a purported taped confession.
Barnes formerly worked for Mitzi Bickers, a political consultant and pastor, who once worked for the city as director of human services. Bickers, who has not been charged, has business ties to Mitchell. Her records were subpoenaed from the city by federal prosecutors in connection with the bribery probe.
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