Shamsud-Din Bahar Jabbar appeared to be living a quiet but dutiful life of work and faith amid Houston’s sprawling diversity: a veteran of the U.S. Army who studied information technology, converted to Islam and recently held a six-figure job.

Little in his outward persona suggested someone who could be responsible for what the authorities described as a brutal terrorist attack along one of the most famous streets in the United States on New Year’s Day.

In a white pickup rented in Houston, authorities said, Jabbar rammed through a crowd of revelers around 3 a.m. on Bourbon Street in New Orleans before opening fire, killing at least 15 people in one of the nation’s worst terror attacks.