Federal prosecutors in Washington today began defending the government’s new case against four former Blackwater security guards charged in a 2007 shooting that left more than a dozen Iraqi civilians dead.

The guards pleaded not guilty today in Washington federal district court to charges that include voluntary manslaughter. The government first brought the case in 2008.

A Washington federal judge tossed the government’s original indictment after concluding that prosecutors improperly relied on protected statements the guards gave after the shooting in Nisour Square in Baghdad. Prosecutors filed the new charges in October.

Lawyers for the guards are again challenging the indictment, claiming it was based on information tainted by the guards’ protected statements. Senior Judge Royce Lamberth of U.S. District Court for the District of Columbia began hearing arguments and testimony today on that challenge in sealed proceedings known as a Kastigar hearing.

For the case to survive, prosecutors must prove the indictment wasn’t based on tainted evidence. The Kastigar hearing is expected to last several weeks. If the indictment stands, a trial is scheduled for June.

The government initially charged five Blackwater guards in the shooting in Nisour Square in Baghdad. At the time of the shooting, the guards were providing security under a contract with the U.S. Department of State.

U.S. District Judge Ricardo Urbina dismissed the case in December 2009, citing the use of the guards’ protected statements. The U.S. Court of Appeals for the D.C. Circuit revived the case in 2011 and gave the government another chance to bring charges. Lamberth took over the case after Urbina retired.

On Sept. 30, prosecutors told the court they were dropping the case against one of the defendants, Donald Ball, as the government prepared to bring another indictment. The four remaining defendants are Paul Slough, Nicholas Slatten, Evan Liberty and Dustin Heard. They’re charged with voluntary manslaughter, attempt to commit voluntary manslaughter and other related crimes.

Slatten, represented by Thomas Connolly and Steven Fredley of Wilshire & Grannis, is also pursuing a separate motion to dismiss the case against him, arguing the statute of limitations ran out for the government to bring a new indictment. Slatten’s position is the D.C. Circuit’s 2011 reinstatement of the prosecution only applied to his co-defendants, while the government contends it applied to all of the guards.

Slatten, Slough, Liberty and Heard were in court for today’s hearing.

Before Lamberth closed the courtroom, Assistant U.S. Attorney Anthony Asuncion said the government made an unsuccessful plea offer to the defendants in late October. Under the terms of the deal, he said, the defendants would plead guilty to two counts of voluntary manslaughter and attempt to commit voluntary manslaughter.

Asuncion said Heard’s lawyer, David Schertler of Schertler & Onorato, formally rejected the offer. Asuncion said he assumed the other defendants implicitly rejected the deal, which expired Nov. 25, by not responding.

Slough is being represented by Brian Heberlig of Steptoe & Johnson. Liberty’s lead attorney is William Coffield of the Coffield Law Group.

Contact Zoe Tillman at ztillman@alm.com.