Navy officer charged with killing his wife with a crossbow goes on trial in N.O.

At first, New Orleans police believed the killer seized an ink pen and stabbed Mary Lou Marx, a Navy officer’s wife, once in the face and again in the chest until she fell dead on her bedroom floor.

But the next day, the coroner made an unusual discovery: Two arrows, fired by a crossbow, caused the wounds that killed Marx on May 25, 2011.

Her husband, David Marx, then a Navy chief petty officer, is standing trial this week for allegedly shooting her with the crossbow. He is charged with second-degree murder, facing an automatic sentence of life in prison without hope for parole if he is found guilty as charged.

The couple’s 12-year-old son first found his mother’s body at their home on Nunez Street in Algiers. When she didn’t arrive to pick him up from school, he caught a ride home, looked through the window and saw her lying in a pool of blood on the bedroom floor.

The coroner determined she’d been killed hours earlier, at 8 a.m., according to court records.

Detective Barrett Morton wrote in his report that the killer had staged a fake burglary: Cabinets and drawers were open, but the contents were still inside. Televisions and laptops were left undisturbed, in plain view. The door was locked and required a key to open it. There was no sign of forced entry.

Morton tried to call David Marx, then stationed in Norfolk, Va., over and over but got no answer. Navy investigators tried to track him down, also to no avail.

David Marx returned the detective’s calls the next day. He said he’d been in Florida and his phone had stopped working. The detective told him his wife had been killed.

“Marx did not ask how she died, or what had taken place in New Orleans,” Morton wrote in his report.

Marx had been a sailor since 1987. He was stationed, for a time, in the New Orleans area, and he and his wife bought their pink shotgun house on Nunez Street in Algiers Point in 2007, according to court records.

At the time of the murder, neighbors told The Times-Picayune that David Marx was preparing to retire from the military and move back to New Orleans with his family. His wife, the neighbors said, had been busy preparing the house for his return.

Marx first said he had not been in New Orleans on the day of the killing. But he changed his story days later, after two witnesses came forward to dispute it. He wrote in a statement that he and another woman had driven from Virginia to Florida to go to a museum. The day before his wife was killed, he wrote, he drove to New Orleans but only “to sightsee” and “look around the area,” then drove back to Norfolk, he wrote.

The two witnesses, who had been out separately on the street that morning, both said they had seen a middle-aged man emerge onto the street, covered in mud. He looked up and down the block, then got into a white Ford Escape with Texas plates — the exact sort of vehicle Marx drove. Both men said they watched as he changed his clothes inside the SUV, still parked by the curb, then drove away.

One of the men picked out Marx’s photo from a lineup.

The Naval Criminal Investigative Service, the Navy’s internal law enforcement agency, arrested Marx two days after the killing.

Marx maintains his innocence. Prosecutors offered him a chance to plead guilty to manslaughter, which carries a maximum sentence of 40 years in prison. Marx refused the plea deal.

His team of attorneys — Frank DeSalvo, Bruce Netterville and Brigid Collins — declined to say on Monday what their defense strategy will be.

The defense attorneys and prosecutors Fran Bridges and Payal Patel picked 12 jurors on Monday in Criminal District Court Judge Ben Willard’s courtroom.

The trial will resume on Tuesday morning with opening statements.