ATLANTA — An Atlanta man who threw a concrete block through a city contractor's window to discourage him from talking to federal investigators was sentenced to prison Monday for obstructing their bribery probe.

Shandarrick Barnes, 41, had pleaded guilty in November to obstructing justice. He's the fourth person to receive a prison sentence after entering a guilty plea in the ongoing federal investigation into a pay-to-play scheme for city contracts.

U.S. District Judge Steve Jones initially said he would sentence Barnes to serve three years and one month in federal prison. He then reduced that to two years and eight months to give Barnes credit for five months spent in state custody because of this incident. Jones also ordered Barnes to serve three years of supervised release following his prison term and to pay $1,500 in restitution.

Federal prosecutor Kurt Erskine said Barnes used "mob-like tactics" to try to keep construction contractor Elvin R. Mitchell Jr. from cooperating with investigators.

Mitchell told people that IRS and FBI agents were asking questions after investigators approached him in July 2015 to discuss corruption allegations and potential tax improprieties. In an interview on Sept. 2, 2015, Mitchell told investigators he'd paid "up-front money" for city contracts. He met with investigators again days later.

Barnes threw a concrete block with the message "ER, keep your mouth shut!" written on it through a window in Mitchell's home early on Sept. 11, 2015, Erskine said. When Mitchell went outside, he found dead rats on his porch, on his car and in his mailbox.

Barnes admitted to federal agents during interviews last year that he had thrown the block, though he said he didn't leave the rats. He told them he knew Mitchell was cooperating with the investigation and that agents had asked about Mitchell's taxes and payments Mitchell made to businesses associated with Barnes' employer, Mitzi Bickers.

Barnes said he took action on his own to get Mitchell to stop talking because he was afraid Bickers' business could be negatively affected, which could threaten his own income, according to Erskine.

Barnes' attorney, Bill Morrison, acknowledged his client's behavior was serious, but said Barnes panicked and made a mistake.

Barnes said he feels "very remorseful" and apologized to Mitchell and his family.

Mitchell pleaded guilty in January 2017 to conspiratorial bribery and money laundering charges. He was sentenced in October to serve five years in prison and ordered to pay more than $1.12 million in restitution. His lawyer said he was cooperating with investigators.

Another city construction contractor, Charles P. Richards Jr., was sentenced in October to serve two years and three months in prison and pay $193,000 in restitution. He had pleaded guilty in February 2017 to a conspiratorial bribery charge.

Prosecutors last month obtained an indictment against Mitzi Bickers, who had helped former Atlanta Mayor Kasim Reed win election in 2009 and was hired in February 2010 as the city's director of human services, a job she held until May 2013. Bickers faces charges including conspiracy to commit bribery, money laundering, wire fraud and witness tampering.

Bickers is accused of soliciting and accepting payments from Mitchell, Richards and their companies in exchange for helping them get city contracts. Prosecutors say she accepted nearly $2 million in payments from 2010 to 2015. Prosecutors also say Bickers cooperated with others to threaten Mitchell to keep him from talking to federal investigators.

Bickers pleaded not guilty to the charges last week and was released on bond.

She was the second former city official charged in the corruption investigation. Former chief procurement officer Adam Smith pleaded guilty in September to accepting bribes in exchange for lucrative city contracts and was sentenced in January to two years and three months in federal prison.