[Read: U.N.C. Charlotte Student Couldn’t Run, So He Tackled the Gunman]

In recent years, reports that some perpetrators of mass shootings had autism has left an impression that it is associated with premeditated violence. But experts have said there is no evidence that people with autism are more likely than other groups to commit violent crimes, and that in the case of mass shooters, autism may simply be existing side by side with other factors that can prompt violence, like psychopathy or a history of trauma.

As a child, Mr. Terrell was studious but stubborn, distanced from people his age, Mr. Rold said. Then, when he was 15, his mother died after a battle with breast cancer that had lasted for most of his childhood.

His grandfather said that he had always been a bit withdrawn, but was especially so after his mother died.

“He wasn’t a happy person,” Mr. Rold said. “It wasn’t that he didn’t laugh or didn’t ever smile, but I would say less so than normal. He didn’t have highs and lows, he wasn’t outgoing and bubbly, but then he didn’t seem to be depressed. I think he felt that life had dumped on him losing his mother. The first thing he said when she passed was: ‘It’s not fair.’”

After his mother’s death, Mr. Terrell moved to North Carolina with his father, where he enrolled in high school, and then at Central Piedmont Community College in Mecklenburg County, which he attended from the fall of 2015 to last spring. His grandfather said his grandson was interested in languages, and had taught himself French and Portuguese using a computer program.

The last Mr. Rold had heard, his grandson wanted to be an accountant, like his father, but wanted to work in South America.

Mr. Terrell enrolled at U.N.C. Charlotte, and took a course described by the instructor as the anthropology and philosophy of science. It met at 5:30 p.m. in Kennedy Hall.