From the moment she learned that her son had coldly and calculatingly shot and killed a former co-worker in Midtown, the mother of Jeffrey T. Johnson has replayed every reel of his life from birth to boyhood and beyond, searching her memory for something that might help explain why.

She thought back to when her son, then in sixth grade, was struck by a car and suffered head trauma that nearly killed him.

She thought of his service in the Coast Guard, where he became an expert marksman, and of how a talent had been put to such a regrettable use.

“I don’t blame police in New York for shooting my son because he killed somebody, but for me, he hasn’t changed. He’s still the kindhearted, caring person who loved all kinds of animals and I’m sure he loved us,” she said through sobs. “You know a mother always tries to look for the best in you.”

She learned of her son’s involvement the same way that most had; on Friday morning, she and her husband were watching the news on television. The couple heard the name “Jeffrey Johnson” and caught the words “Hazan Imports,” the business on West 33rd Street where their 58-year-old son had designed women’s T-shirts. Right away, they knew, she said.

Ms. Johnson, who is in her 80s, asked The New York Times to withhold her first name and the town in Georgia where the couple lives, to protect their privacy.

Investigators say they believe that Mr. Johnson killed his former co-worker, Steven Ercolino, 41, because, in part, he blamed him for his job loss. In Mr. Johnson’s mind, he would not have been laid off if Mr. Ercolino, a salesman and an account executive at Hazan, had sold more of the clothing line designed by him, the police said.

Two police officers shot and killed Mr. Johnson on the sidewalk in front of the Empire State Building after he pointed the gun at them. Nine bystanders were hit by police bullets or fragments, according to the police.

In an hourlong conversation, Ms. Johnson spoke of her agony in trying to comprehend the shocking descent of a little boy who loved the Boy Scouts and animals, and who grew into a patriotic and thoughtful man.

Mr. Johnson was born in Japan. His family came to the United States when he was 10 months old, and he grew up in Georgia before going to art school in Florida and then making his way to New York City more than a decade ago. “He had a kind life,” his mother said.

Maybe the head injury he suffered as a boy caused him to “snap” all these years later, she said.

'I don’t understand what snapped in him to do what he did'
He had been struck by a car when he was about 11. He was in a coma for five days and doctors did not expect him to live, Ms. Johnson said.

“The doctors told me once that they would be very surprised if he didn’t have any aftereffects,” she said. “But he seemed to recover all the way. He was not acting funny, but you know, when you get older, your body, especially if you are injured, will kind of deteriorate.”

“I don’t know,” Ms. Johnson added. “This may be some kind of excuse. I don’t understand what snapped in him to do what he did.”

Her son had to drop out of the Boy Scouts after being struck by the car. He had to wear a helmet to protect his head from further injury, she said.

After attending Ringling College of Art and Design in Sarasota, Fla., he joined the Coast Guard and got married. After four years he and his wife divorced, about three decades ago, Ms. Johnson said.

Mr. Johnson moved to New York to be at the center of the art scene. He spent hours in museums and revered the Dutch painter Vermeer, she said.

He was enthralled, too, with Pale Male, the red-tailed hawk that made its home near Central Park. He took dozens of photographs of the hawk and mailed them to her, she said.

After the Sept. 11 terrorist attacks, Mr. Johnson, who lived in the city at the time, sought to return to the Coast Guard, she said.

Citation for marksmanship
“He was very patriotic,” his mother said. “He wanted to fight again, but the government told him he was too old.”

She said her son had earned a citation for marksmanship while in the Coast Guard — a poignant sidelight to his actions on Friday. But she found some small comfort in that her son did not shoot any of the bystanders who were wounded.

“You don’t know how much relief that gave me, that my son didn’t shoot anybody else, not that shooting one person was right,” she said.

Though she had not seen him for 22 years (he had not returned home since 1990), Mr. Johnson used to call her every Sunday. He rarely spoke about his work. He never told her that he had been laid off from Hazan. Instead, he told her he quit because he did not get along with a co-worker, she said.

“He is hard on himself,” she said. “He is a perfectionist and he is hard on himself, but he is also hard on others, too. He just cannot compromise.”

The last time she spoke to her son was April 6. He called to wish her a happy birthday. He had not made his weekly call since a Sunday this past January, when she asked if he needed any help with money and questioned how he could afford to live in New York City.

“That just made him very angry,” she recalled. “He said, ‘Mama, by right I ought to be building a house for you. That’s what the firstborn should do.’ He always had a self-guilt that he didn’t take care of his parents the way he wanted to.”

Just before the falling out, he sent her a two-page typed letter.

Much of the letter focused on the death of Romeo, his cat. He had fretted so much over the cat’s health that at one point, Romeo’s veterinarian expressed worry about her son, she said.

At the time, the veterinarian did not realize that Romeo was suffering from a rare and aggressive form of cancer. Mr. Johnson spent months trying to save and treat the cat. In his Jan. 10, 2012, letter to his mother, he wrote that he had to let the cat go: “All I can do now is try to give him a peaceful death.”

He went on to detail how the veterinarian had euthanized the cat six months earlier, she said.

“I felt like such a moron,” he wrote. “For years, he had been trying to tell me that something was wrong. And I hadn’t been able to help him.”

Life seemed dimmer since his cat died
He wrote, “The doctor let me use her office and I wrapped Romeo in my best Fendi jacket so he wouldn’t shiver.”

Though Mr. Johnson still had another cat, Tiger, his mother said, he said that life seemed dimmer since Romeo died, and he wrote that he “honestly would have traded places with him.”

“I am astonished by how much I miss him,” he wrote. “He just filled every room in the apartment. Nothing seems special without him around. It embarrasses me that I feel this way. Life is bigger than one cat or me or you. But I can’t shake the feeling that life has been diminished tenfold by Romeo’s parting.”

“Don’t worry,” the letter ended. “I am all right. Jeffrey.”

“But evidently,” his mother said, “he was not.”