Another man who served with Sergeant Bellino and became a close friend said he had little outside the military. “Guys like Steve have been warriors so long, they are almost addicted to being deployed,” said a man who served with Sergeant Bellino and became a close friend. “They come back to the United States and there is no place for them,” he said. “My heart hurts for everyone involved.”

While not deployed, Sergeant Bellino worked overseas as a private security contractor, his lawyer said, doing what were effectively civilian deployments. Soldiers said those deployments were in Iraq. In his free time he studied combat tactics like knife fighting and door breaching, the longtime friend said. He never drank or smoked and was extremely fit.

Sergeant Bellino had no children and never married. His only company at home was a single, sprawling house plant, which was all his lifestyle would allow, his friend said, but it had its own room and he lavished it with attention. A Facebook page with Sergeant Bellino’s name, linked to his family members, was bare except for endorsements of a few Ohio restaurants and the author Ayn Rand.

A woman who answered the phone at a house belonging to his twin brother, declined to identify herself, but said, “We’re heartbroken, he was such a loving son and brother and uncle.”

Image Steven Bellino in a photograph provided by an Army colleague.

In 2011, Sergeant Bellino became an F.B.I. special agent, which his friend said was a lifelong goal, but Mr. Bellino told his friend he found himself stuck in an office doing paperwork. He resigned after two years, the F.B.I. said. After leaving, he wanted to go back to the Special Forces full time, but could not find a slot, his lawyer said. Instead he went to the Air Force, which brought him in as a technical sergeant — a rank similar to the one he held in the National Guard.

On June 30, he showed up at the 342nd Training Squadron at Lackland Air Force Base on Joint Base San Antonio to start the demanding pararescue program. In August, an Air Force trainer said Sergeant Bellino failed part of a physical endurance test in which he had to swim the length of a pool underwater, according to Mr. Conway, and became angry because he felt he was being treated unfairly and forced out of the program.