Federal prosecutors announced Tuesday that they secured a fourth guilty plea in an ongoing public corruption investigation at Atlanta City Hall.

Shanderrick Barnes

Shandarrick Barnes—a 41-year-old convicted felon who was indicted by a federal grand jury in August in the ongoing corruption probe—pleaded guilty Tuesday to obstruction of justice, said U.S. Attorney Byung J. “BJay” Pak.

Pak said Barnes threw a concrete block through the window of E.R. Mitchell's home “to get him to shut up” as federal agents interviewed contractors in 2015.

“Instead, that violent act made Mitchell even more resolute in his cooperation with federal law enforcement,” Pak said.

Elvin R. Mitchell Jr., owner of E.R.Mitchell Co., Cascade Building System, E.R. Mitchell Group and E.R. Mitchell Construction, pleaded guilty in January to a single bribery conspiracy charge for paying more than $1 million to an unidentified individual in return for city contracts. He was sentenced to five years in prison in October and ordered to pay more than $1.1 million in restitution.

Federal prosecutors said that, days after Mitchell confessed to federal agents in 2015 to paying to secure city contracts, Barnes lobbed a concrete block bearing the words “ER, keep your mouth shut!” through a plate-glass window and left dead rats on Mitchell's porch, in his car and in his mailbox.

When federal agents interviewed Barnes, he admitted he threw the block and that he was aware the IRS was investigating Mitchell and had asked about payments Mitchell made to Barnes' employer. Prosecutors said Barnes told federal agents at the time that he feared Mitchell's cooperation “would negatively affect his employer's business.” His employer is a political consultant and former city employee who had business ties to Mitchell, according to The Atlanta Journal-Constitution.

Barnes is the fourth individual to plead guilty in the pay-to-play investigation of contracting practices at Atlanta City Hall. In February, a second city contractor—Charles P. Richards Jr., owner of C.P. Richards Construction Co. and C.P. Richards & Associates—pleaded guilty to a criminal information accusing him of conspiring with Mitchell. Richards paid at least $185,000 in bribes to an unidentified individual, believing that some portion of the money would be paid to city officials who could influence the city's contracting and procurement process, according to the criminal information. Richards was sentenced to serve 27 months in prison last month, and ordered to pay $193,000 in restitution.

In September, Adam L. Smith, who was Alanta's chief procurement officer from 2003 until last February, was charged with a single conspiracy count in a criminal information—a form of charge federal prosecutors make in lieu of an indictment that generally signals a plea deal has been reached.

According to the criminal information, Smith between 2015 and 2017 took $30,000 from an unnamed contractor who routinely met with him at local restaurants in order to solicit city business. At each of those meetings, the duo discussed procurement projects, bids and solicitations the contractor was interested in, according to the information.

Smith routinely received a $1,000 bribe at those meetings, the criminal information said.

In addition to supplying the vendor with details about the bid proposal, Smith would approve the contract whenever a company or joint venture the vendor was associated with secured the winning bid, the information said.

Federal prosecutors announced Tuesday that they secured a fourth guilty plea in an ongoing public corruption investigation at Atlanta City Hall.