LEFLORE COUNTY, Miss. — Military investigators picked through the still-smoking wreckage of a Marine Corps transport plane on Tuesday, trying to learn what caused the aircraft, part of a Reserve unit based in New York, to plunge into a soybean field in the Mississippi Delta, killing 16 service members.

The KC-130 plane burst into flames on impact Monday afternoon, leaving a charred furrow in the otherwise idyllic, deep-green landscape of waving bean, corn and cotton plants along United States Highway 82, and scattered fiery debris and bodies across farmland and rural roads.

Among the first witnesses at the scene was David Habig, a crop-duster pilot who flew low over the wreckage. “Lo and behold, all I see are bodies out in the bean field,” he said. “They were everywhere. It was horrific. I’d never seen anything like it.”

The plane, carrying 15 Marines and one Navy corpsman, belonged to Marine Aerial Refueler Transport Squadron 452, or VMGR-452, nicknamed the Yankees, a Reserve unit based at Stewart Air National Guard Base in Newburgh, N.Y., the Marine Reserve said on Tuesday. The flight, which took off from Marine Corps Air Station Cherry Point in North Carolina, was headed to Naval Air Facility El Centro in California and was transporting personnel and equipment, the Reserve said in a statement.