WASHINGTON -- Federal prosecutors in Washington likely face an uphill fight in their case against five indicted Blackwater Worldwide guards who are expected to surrender to authorities Monday.

The case is crucial for the Justice Department, which is struggling to show it can hold U.S. security contractors accountable, as well as for Iraqi leaders, who have just stripped legal immunity from foreign guards. The five Blackwater guards, protecting a State Department convoy, were involved in a Sept. 16, 2007, shooting incident...