The Justice Department brought new charges Thursday against four former Blackwater Worldwide security guards accused of taking part in a shooting in Baghdad six years ago that killed 14 unarmed civilians, wounded 18 and enraged public opinion in Iraq. A federal grand jury…returned a fresh indictment charging the four guards with voluntary manslaughter and other crimes in the shooting in Nisour Square…Charges were first brought against six Blackwater guards in 2008. In 2009, U.S. District Judge Ricardo M. Urbina said that federal investigators and prosecutors had obtained the indictment by using tainted evidence…Two years ago, the U.S. Circuit Court of Appeals for the D.C. Circuit revived the prosecution by ruling unanimously that Urbina had misinterpreted the law.