He was the son of a veterinarian, the product of a middle-class neighborhood where families tend to their yards and keep to themselves. That has left some who knew him at a loss about why Colton Joshua Tooley, three months past his 19th birthday, tried to shoot up the University of Texas campus.
A day after Tooley opened fire with an AK-47 at the sprawling campus and ultimately used it to kill himself, some friends and acquaintances said he showed no signs that would have predicted such violence.
"He never seemed weird or like he would end up doing that," said Devon Sepeda, a UT student who graduated from Austin's Crockett High School in 2009 with Tooley, who finished seventh in his class of 400.
High-achieving students can become dangerous if they are isolated and without balance in their lives, said James Alan Fox, a professor of criminology at Northeastern University known for his research on school shootings and other mass murders.
The fact that Tooley apparently didn't have a Facebook account "reflects a certain degree of isolation" that may be a clue to his behavior, he said.
"There are students for whom academics is not everything," Fox said. "They have friends. They have hobbies. They can put things in perspective. Not everyone can do that."
At UT, Tooley was a sophomore majoring in math and actuarial studies and had already taken classes in calculus and linear algebra.
"His teachers recall him with words such as `brilliant,' `meticulous' and `respectful,"' Crockett principal Craig Shapiro wrote in a statement.
Neighbors in the modest South Austin neighborhood where Tooley grew up recall a quiet young man who was rarely seen except when shooting baskets in his driveway.
"He was a gentle spirit," neighbor C.J. Drake said. "He really meant no harm to anyone else."
Tooley, the only child of a veterinarian father and a mother who is licensed to operate a daycare, kept living with his parents even after entering UT, according to Drake, who has lived across the street from the family for more than two decades.
Heading across campus Tuesday morning, Tooley fired shots but didn't hit anyone as students and university employees scrambled for cover. With police closing in, he wound up in a campus library and turned the weapon on himself.
Jeffrey Graves, UT's associate vice president of legal affairs, said Wednesday that the university had no record of Tooley being flagged for behavioral concerns before the incident.
UT has a behavioral assessment team, which meets to discuss and address student behavioral issues, and an advice line that takes calls about concerns anyone might have about an individual, university officials said.
"He was not on our radar," Graves said. "We checked into that as soon as we had the name. Not in any of our databases."
Although the Tooley family kept to themselves and wasn't particularly well known, neighbors rallied around them Tuesday night, putting more than a dozen candles on the sidewalk in front of their home. Family members responded by briefly emerging to acknowledge the vigil.
"Our neighborhood is heartbroken," Drake said. "We know that they are a very close and loving family. It's a mystery to everyone why such a promising young man would perform such a desperate act."