NEW YORK — At the start of his Air Force career, Devin P. Kelley was picked for a demanding and selective intelligence analyst school. He walked into his first Monday of class with a crisp blue uniform, shined shoes, and for perhaps the first time in years, with hope. It didn’t last.

Two years later, he found himself on the run, in a bleak El Paso bus station at midnight trying to catch the first Greyhound back home after flunking out of school, being charged with assault, and escaping from a psychiatric hospital.

For Kelley, who last Sunday opened fire on a rural Texas church, killing 26 people, the Air Force could have been a turning point — a source of discipline and direction that he had not embraced in a troubled childhood.

But military records and interviews with fellow airmen show that despite repeated chances, his career fell apart under the weight of his depression and rage, at a time when his mind was churning with half-laid plans to kill his superiors.

After only a few months in the service, Kelley slid back into a long decline that left a wreckage of broken relationships, criminal convictions, and eventually bloodshed.

“The Air Force tried to give him chances, but he was just problem after problem after problem,’’ said Jessika Edwards, a former Air Force staff sergeant who worked with Kelley in 2011, near the end of his career.

“He was a dude on the edge,’’ Edwards added, noting that he would appear at informal squadron social functions dressed all in black, with a black trenchcoat. “This is not just in hindsight. He scared me at the time.’’

Even after he left the military, he contacted Edwards on Facebook with disturbing posts about his obsession with Dylann Roof, the Charleston, S.C., mass murderer.

Edwards said the military had tried counseling and tough love, but nothing seemed to work. When punished for poor performance, Kelley would cry, scream, and shake with rage, vowing to kill his superiors, she recalled.

His temper was so unsettling that she warned others in the squadron to go easy on him or he was likely to come back and “shoot up the place.’’

The Air Force, like the civilian world, is often ill-equipped to intervene before violence occurs. Though Kelley’s behavior raised flags, commanders say they have limited options until a crime is committed.

Even then, the priority is more often on getting problem troops out of the military, giving little thought to the possible impact on society. After facing intense criticism for its failure to report Kelley, the Air Force has opened an investigation into the case and many questions remain about what more it could have done.

Growing up in New Braunfels, Texas, Kelley earned mostly C’s and amassed at least seven suspensions for insubordination, profanity, dishonesty, and drugs, according to school records.

He enlisted in the Air Force after high school in 2009. Based on above-average aptitude test scores, he was picked to become a fusion analyst — an intelligence specialist trained to interpret and communicate the latest information on enemy tactics.

In spring 2010, after two months of basic training, he arrived at Goodfellow Air Force Base near San Angelo, Texas, for the six-month intelligence technical school. Kelley washed out before graduation, for what the service said were academic reasons.

The Air Force made him a traffic management apprentice, a job that includes moving people and freight and requires a minimal aptitude score. He was sent in 2011 to Holloman Air Force Base in New Mexico

His squadron wrote up the airman for multiple infractions, Edwards said, trying to make a case to discharge him for poor performance. Before it could do that, in April 2012, Kelley was arrested and detained after he pointed a gun at his wife, hitting, and choking her, and hit his baby stepson, fracturing his skull.

His wife filed for divorce that year.

While Kelley awaited court-martial, the Air Force sent him to a civilian psychiatric hospital in Santa Teresa, N.M., where, according to local emergency dispatch records, he was given medication for depression, anxiety, and attention deficit hyperactivity disorder, and was considered a “high-risk patient.’’

On the night of June 7, 2012, Kelley escaped.

His counselor at the hospital called police, according to a police report, warning that Kelley had talked about killing his chain of command in the Air Force and had told other patients that he had recently bought guns online.