Andrew Lincoln (Rick Grimes) and Danai Gurira in "The Walking Dead"

The death of a stuntman on the set The Walking Dead has temporarily halted production of the popular AMC series. John Bernecker, age 33, was fatally injured while rehearsing a fight scene that was supposed to end with a routine fall from a balcony. Instead, questions abound as to how a seemingly simply stunt could go so horribly wrong.

Mr. Bernecker was a veteran stuntman, described by Conrad Palmisano, former president of the Stuntmen’s Association of Motion Pictures as “very qualified, a good guy, focused and competent.” He had also worked in the more senior role of stunt coordinator, meaning he would have been responsible for designing and prepping stunts and would play a key role in ensuring the safety of other stuntmen.

According to a report from the Coweta County Sheriff’s Office, Bernecker was supposed to fall from a balcony over a railing onto a pad made of a layer of 22-inch boxes, port-a-pit pads, and a large pad. Actor Austin Amelio, who plays Dwight on the series, was on the balcony with Bernecker prior to the deadly accident. He told police he asked Bernecker if he’d ever done a fall like that before. The stuntman said he’d done a few but never from that high up, and he “seemed a little nervous.”

When Bernecker gave a thumbs-up to signal he was ready, filming began. Bernecker got most of the way over the railing and then appeared to try to stop the fall by grabbing the railing with both hands, but he hit the balcony, causing him to release his grip and spin upside down as he fell, the report says. Bernecker landed a few inches from the pad. An on-set medic immediately responded and requested that 911 be called. Bernecker was then flown by helicopter to an Atlanta hospital.

Bernecker died of blunt force trauma at Atlanta Medical Center. His family released a statement saying that they would be donating his organs. “Something obviously went wrong,” says Palmisano, who adds that the cause might ultimately never be known. “It’s never a black and white thing. It’s always a pinch of this, a dash of that, then something tragic happens.”