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.


And to a more recent time, when his beloved cat Romeo died in his arms, the sickly and shivering pet cradled in “his best Fendi” suit jacket, his mother said during a phone interview on Monday. The death of that cat left him distraught; he wrote in a letter that since Romeo’s passing, “life has been diminished tenfold.”


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.


“I know there are a lot of Jeffrey Johnsons in the world and a lot of Jeffrey Johnsons in New York City, but when they said the company he used to work for,” she said, “I just went to pieces.”


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.


Ms. Johnson believes that her son wanted the officers to kill him. “I believe that he turned and pointed the gun at them to make sure that they would shoot him and he would die,” she said.


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.


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.


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