A federal appeals court has ordered a new trial in a lawsuit filed by the family of a Texas soldier who was killed and others who were injured during a live-fire training exercise in Hawaii.

The 9th U.S. Circuit Court of Appeals ruling overturned a jury verdict that found the manufacturer of mortar cartridges not liable for causing the 2006 explosion that killed Staff Sgt. Oscar Rodriguez.

The 27-year-old from Beeville, Texas, was hit by shrapnel at the Pohakuloa Training Area on the Big Island. He was supervising the firing of two mortars when a shell detonated in the cannon. The blast seriously injured Samuel Oyola-Perez, Julius Riggins and Wilfredo Dayandante.

The lawsuit was filed in 2008 against General Dynamics Armament and Technical Products Inc., claiming the shell was defective. The plaintiffs appealed the jury’s 2010 verdict.

The appeals court issued a ruling on March 7 that the trial court was wrong to allow an Army investigator to give testimony as a lay witness that could only be provided by an expert. The investigator, Philip Leong, claimed the explosion was probably caused by the soldiers. He was General Dynamics’ only witness.

“Here, the district court erred when it allowed Leong to offer specialized and highly technical testimony about the cause of the explosion,” the 9th Circuit panel’s opinion states.

One of the three judges dissented, writing, “a retrial is no more than a second bite at the same apple.”

Attorneys for the defendants didn’t respond to requests for comment.

“After Oscar died, the Army came to my home and told me that a crack in General Dynamic’s mortar shell caused the explosion,” said Rodriguez’s wife, Stephanie Rodriguez, who lives in Kansas City, Mo. “This was the official explanation provided to my family by the Army. The Army was very clear that the soldiers did not cause the explosion.”

Her husband joined the Army in 1996 and served in Iraq for 13 months before being assigned to Hawaii. The couple has a son, Jacob, who is now 7.

“Oscar died seven years ago and this has been a very, very long journey,” the widow said. “We will see this through and find justice in Oscar’s memory, and for the other soldiers and families.”

Dayandante was disabled after the blast and died of a heart attack in May 2009, said David Larson, lead trial attorney for the plaintiffs. He said lawyers haven’t been able to directly link the 28-year-old’s death to his injuries in the explosion.

His mother pursuing the lawsuit on his behalf.