An appeals court on Friday resurrected the case against four Blackwater Worldwide guards involved in a 2007 shooting in a Baghdad public square that killed 17 Iraqi citizens.

A federal trial judge in Washington, Ricardo Urbina, threw out the case on New Year's Eve 2009 after he found the Justice Department mishandled evidence and violated the guards' constitutional rights.

But a three-judge panel of the U.S. Court of Appeals ruled Friday that Urbina wrongly interpreted the law. It ordered that he reconsider whether there was any tainted evidence against four of the five defendants —former Marines Evan Liberty of Rochester, N.H.; Donald Ball of West Valley City, Utah; and Dustin Heard of Knoxville, Tenn.; and Army veteran Paul Slough from Keller, Texas.

The Justice Department has dismissed charges against the fifth defendant, Nick Slatten, a former U.S. Army sergeant from Sparta, Tenn.

Blackwater security contractors were guarding U.S. diplomats when the guards opened fire in Nisoor Square, a crowded Baghdad intersection, on Sept. 16, 2007. Seventeen people were killed, including women and children, and 20 others wounded in a shooting that inflamed anti-American sentiment in Iraq.