(CNN) -- Two by two, the tandem skydivers leapt into the clouds over southern Mississippi, a routine plunge from thousands of feet in the air.
James "Jimmie" Horak Jr. and his student were the last out of the plane Saturday morning. A videographer captured the moment when the veteran instructor opened his parachute, shifting a rapid freefall into a slow descent.
But something tragic happened in the final seconds of the drop. Horak, 56, and his student never landed at the airport where they were supposed to.
Instead, Horak's body was found in heavy mud in a swampy wooded area about a mile from the airport in Lumberton, Lamar County Sheriff Danny Rigel said.
His student, a 26-year-old man whose name was not released, was in critical condition with broken bones and head injuries.
It's unclear what went wrong. But based on evidence on the ground, Horak cut away the main parachute and deployed his backup, Gold Coast Skydivers owner Leanne Igo said.
"We just know that the main was cut away and the reserve was deployed," Igo said. "Everything else beyond that is speculation."
Rigel said the others on the ride noticed there was some kind of equipment trouble, perhaps a problem with the lines.
When the other students landed at the airport in Lumberton and noticed the pair weren't with them, they started a search that quickly included 30 skydivers on foot, a skydiving plane, a helicopter and local authorities, Igo said.
The son of a nearby landowner eventually found Horak and the student while riding his Four Wheeler in the woods, she said. Horak and the student were so far inside the woods that "there was no way anybody could spot them from overhead."
Deputies had to carry them out for a "considerable distance" to get them out of the woods, and the student was then airlifted to Forrest General Hospital in Hattiesburg, Rigel said.
The Federal Aviation Administration will inspect the parachutes to determine if they were properly rigged by a qualified parachute rigger, and if the parachute operation was in compliance with federal regulations, FAA spokeswoman Kathleen Bergen said Sunday.
Local authorities will investigate the event and determine probable cause, she said.
Horak's cause of death won't be known until after an autopsy, likely to take place Monday, Rigel said.
A skydiving fan since the 1970s, Horak served with the Army Special Forces and was a pilot who also worked for the Veterans Administration as a physician's assistant, Igo said.
"Very professional, soft-spoken, kind-hearted, hard worker, a genuine person and highly experienced," she said of Horak. "He had a wonderful wife and three children and everybody who ever met Jim never had anything ugly to say about him. He loved what he did."
Horak was also meticulous about safety, his friend and fellow skydiver Timber McKinney said.
"I've never met a more outstanding instructor in all my years of skydiving, 27 years now," McKinney told CNN affiliate WEAR. "He really emphasized the safety side of it. He was about the fun side of it too, but he would definitely make sure that everyone that he touched understood the rules and that they follow them."
Horak was a safety and training advisor appointed by the U.S. Parachute Association, Igo said. Along with being a tandem instructor, he was a tandem examiner who trained other tandem instructors, she said.