Intensive care nurse Angie Boivin had just tended to a woman whose leg was severed near the hip when she saw her husband Larry lying nearby under an American flag blanket. She says that she was with him when he took his last breath.

Larry Boivin earned a Purple Heart in Iraq in 2004, but he didn’t survive a Union Pacific freight train that slammed into the flat-bed trailer he and other veterans were riding on during a 2012 parade in Midland, Texas. Three other veterans died and more than a dozen people were injured in the crash three years ago this month.

“They used that (train) as a weapon to kill my husband,” Angie Boivin said.

She and 42 other survivors and family members sued Union Pacific Railroad Co. for negligence, saying the railroad knew 10 months before the collision of a defect in the track detection circuitry, which delayed the activation of warning lights, bells and a crossing gate. The problem caused by that defect was further compounded, they allege, by a reduced crossing warning time set by the railroad in violation of a state agreement.

Shortly before trial was to begin in January, 26 of the survivors and families of victims settled for an undisclosed amount with Union Pacific, the nation’s largest railroad with $5 billion in profits last year. A judge dismissed the remaining case in February, and three widows appealed to the 11th Court of Appeals in Texas. Union Pacific must file a response by Dec. 21.

Union Pacific called the collision “tragic for the victims and their families” but denied fault. It pointed to reports from the National Transportation Safety Board and the Federal Railroad Administration, which regulates the nation’s railroads, that found the warning time before the train reached the crossing met the federal minimum. The railroad has not been sanctioned or fined by any state or federal authority as a result of the accident.

Both sides agree the system gave 20.4 seconds warning that day, just above the 20-second federal minimum. The dispute, according to a review of court documents, is over another part of the same federal regulation that also says a railroad “shall” maintain the warning system as designed. The Midland crossing was originally designed for a 30-second warning by a diagnostic team that included railroad, state and Midland city officials, court records show.

The railroad told the transportation board it used a 25-second design for the crossing. Additionally, Union Pacific says that once a federal agency adopts a rail safety regulation, such as warning time, that pre-empts state regulation.

Even if the widows win in court, experts said it is unlikely to lead to a review of warning times at the 129,000 crossing nationwide that were designed for more than 20 seconds.

“I do not see the railroad industry taking responsibility when it’s obvious from the evidence they (Union Pacific) had responsibility,” said Bob Comer, a railroad crossing expert who’s investigated about 400 accidents over 26 years and studied the Midland accident.

Union Pacific declined to respond to specific questions from The Associated Press about the crash and its actions before the tragedy, pointing to its statement denying fault.

The driver of the truck pulling the Midland float said in a deposition that if there had been nine more seconds of warning – in accordance with a 30-second warning – the gate arm would have come down in front of the truck, not behind the cab, and he would have stopped in time.

Instead, the first float crossed safely but the second was trapped on the tracks. The train hit the last 39 inches of the trailer bed going 62 mph, tossing people into the air. Larry Boivin jumped off to the left after telling his wife to jump and pushing her. The force of the impact pushed the trailer, which hit him midair. Angie Boivin injured her back in the fall.

Killed in the tragedy were Marine Chief Warrant Officer 3 Gary Stouffer, 37; Army Sgt. Joshua Michael, 34; Army Sgt. Maj. William Lubbers, 43, and Boivin, a 47-year-old Army sergeant major.

The widows say the case is not about money. They want the railroad held accountable and to help prevent similar tragedies.

When the crossing was designed in 1987, court documents show that a diagnostic team including a Union Pacific representative and state and local officials agreed on 30 seconds of warning time. They said this was necessary because of a road hump at the crossing, traffic lights on parallel streets, a heavy volume of traffic and trains travelling faster than 50 mph.

In 1989, the railroad reduced the warning time for that crossing to 25 seconds, according to information it gave the NTSB. State and local transportation officials, responding to open records requests, found no documents that show Union Pacific got approval from the state to reduce the time.

In 2005, the railroad installed an upgrade to the track detection equipment to accommodate faster trains, and in 2006 it increased the train speeds in Midland to 70 mph, court records show. The upgrade, the widows’ lawsuit alleges, created the defect in the detection system, effectively reducing warning time.

Court records show that 10 months before the accident a Union Pacific contractor told the railroad there was a “critical” problem in the in-track circuitry – the electric circuitry that activated the bells, lights and gate.

Plans were drawn up to correct the problem. But the railroad didn’t follow through, the NTSB said, calling that an “oversight.” Nonetheless, the board’s report says the warning system provided the 20-second minimum as federal law requires, and did not cite the defect as a cause of the collision.

The defect in the track detection circuitry was compounded in March 2012, the widows’ lawsuit contends, when a Union Pacific representative found the warning time set for 35 seconds and dialed it back to 25 seconds because that’s what the railroad’s design called for.

The combination of the reduced warning time and the circuitry defect was “catastrophic,” the lawsuit alleges.

“It is infuriating that this railroad can know there was an issue and just blatantly not fix it,” Angie Boivin said.

Union Pacific said it added time to the crossing signal where the collision occurred in December 2012, a month after the accident.