TUCSON, Ariz.—He was the shy, sweet boy who once bought her a box of Belgian chocolates, loved the Beatles and practiced clarinet with her in his parents' living room. And when 15-year-old Kelsey Hawkes asked him to be her boyfriend, Jared Loughner's face lit up with happiness and surprise. "I was going to ask you!" he exclaimed.

Kelsey Hawkes dated Jared Lee Loughner six years ago. Splash News

That was six years ago. On Saturday, Mr. Loughner allegedly shot and killed six people and wounded 14 more, including U.S. Rep. Gabrielle Giffords.

College classmates and instructors have described behavior over the last year that caused them to fear the young man. And some neighbors of the Loughners have described a reclusive family, with occasional outbursts from Mr. Loughner's father.

"That's not the person I knew, and there were no signs he would become this person," said Ms. Hawkes, now a 21-year-old student at the University of Arizona in Tucson.

She said she couldn't believe it when her sister called to tell her that the boy she dated for 10 months in high school was the suspected shooter in Saturday's attack.

"I was in shock. He was completely normal," she said. "I wouldn't have dated him if there was anything wrong."

Ms. Hawkes's account sheds new light on the earlier life of Mr. Loughner and his parents—which she depicts as a peaceful and happy time in the family. Over the next few years, Mr. Loughner allegedly experimented with drugs and alcohol and left a trail of often-incomprehensible writings online.

Ms. Hawkes said she hadn't seen Mr. Loughner in five years and wanted to make clear that she didn't have anything to do with him now, or who he became.

"Some people are getting the idea that Jared became who he is today because five years ago I 'broke his heart,' " Ms. Hawkes said in an email. "It's not fair to me to pin that on me."

The teens met at a fall football game at Mountain View High School, a sprawling campus of nearly 2,000 students on the northern edge of Tucson. Ms. Hawkes and Mr. Loughner weren't really there for the game. They were there to see friends.

A mutual friend introduced the pair, and they hit it off that night.

"We had a lot of things in common," Ms. Hawkes recalled in an interview.

Both liked classic rock, both played the saxophone and both lived in the same neighborhood and even waited at the same school-bus stop. The tall, skinny sophomore with scruffy blond hair was shy, like her.

"I liked his personality," Ms. Hawkes said. "He was nice, attentive. He was never rude. He had no interest in drugs or alcohol. He was respectful. He would give me compliments and never ignore me."

A few weeks after they met, Ms. Hawkes, a freshman, asked him to be her boyfriend. He immediately said yes. "We always joked about how I'd asked him first," she said. He was her first "real" boyfriend, and she was his first girlfriend.

Soon, the two spent hours a day together, lounging in the school's outdoor plaza for lunch and spending time at each other's houses doing homework or playing instruments. When Mr. Loughner started playing the clarinet, Ms. Hawkes said, "Hey, I want to learn too." Mr. Loughner taught her.

She taught him to make French toast. One morning, he proudly made her a plate of French toast at her parents' home and joked that it was better than hers.

Mr. Loughner's father was quiet, Ms. Hawkes said, but not distant. He spent most of his time restoring old cars, she said. "His dad was always there," she said. "He'd get these old cars and fix them up really nice."

Mr. Loughner's mother worked and would offer the pair snacks and check in on them when she got home, Ms. Hawkes said. "She didn't hover. I guess she did the normal amount of checking," Ms. Hawkes said.

If Mr. Loughner had complaints about his parents, she never heard them. "He admired his mom," she said. "She was really sweet and thoughtful."

The Loughner house was neat and comfortable, with framed family pictures all around, she recalled.

Mr. Loughner became more open and extroverted around Ms. Hawkes. They went to the movies at the Foot Hills Mall and played Super Mario Brothers at his house. He was into videogames, she said, "but not the kind of person who would sit there and play all day."

If anything, he liked his music more. Instruments cluttered his room, and the two planned to take band class together the following year.

But Ms. Hawkes was beginning to feel restless over the summer. There was no big fight, no change in Mr. Loughner's personality. The relationship began to fade, at least for Ms. Hawkes.

"I just wanted to be single," she said. Just before school started, she worked up the courage to tell Mr. Loughner she wanted to break up.

"He was surprised and sad," she said. He asked her why.

After that, Mr. Loughner and Ms. Hawkes broke off communication. They met silently at the bus stop in the morning and sat on opposite sides of the room in band class.

"I knew he was really sad, but he mostly kept it to himself," she said.

In the following years, Ms. Hawkes mainly lost track of Mr. Loughner.

"I just had no way of knowing he would ever do anything like this," she said.The last thing she heard about him was through mutual friends: "I'd heard he was drinking and that he wasn't doing so well."

—Peter Sanders contributed to this article.

Write to Tamara Audi at tammy.audi@wsj.com