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(The following story by Rebecca Cathcart appeared on the New York Times website on September 20.)

LOS ANGELES — He lived a solitary life, working long days and long nights as the engineer of a commuter train that crawled across Southern California, making stop after routine stop. He loved trains, so much that he encouraged teenagers who showed their own enthusiasm for the rails, exchanging text messages while he was at work, one boy asserted last week. That, the authorities say, may have contributed to the worst California train disaster in 50 years.

In the week since a Metrolink passenger train collided head-on with a Union Pacific freight train, conflicting portraits of the engineer, Robert M. Sanchez, have emerged. Mr. Sanchez, 46, who did not brake before the crash, died along with 24 others; more than 130 people were injured. Investigators are considering whether he might have been distracted by sending or receiving text messages at the time.

Accusations that he was sending messages have stirred outrage from blogs and online forums. Some neighbors in La Crescenta, the suburb northeast of Los Angeles where he had lived for three years, said this week that the engineer was reclusive and cold. His home, its shades drawn, with a dirt yard and white walls, stood out from the flowerbeds and colorful houses near it.

But friends and colleagues of Mr. Sanchez described him as warm and conscientious, a mentor to the teenage railroad aficionados who may have been on the receiving end of his text messages that day.

He also struggled with diabetes, some friends said, and long hours on the job made it hard for him to maintain friendships. He carried well-concealed grief, one friend said, after the death of his partner, Daniel Burton, in 2003.

“Rob was very upbeat and very enthusiastic,” said Lilian Barber, 77, a dog breeder in Murrieta who became friends with Mr. Sanchez five years ago when he called her for advice on breeding the Italian greyhound, Ignatia, he had owned with Mr. Burton.

Mr. Sanchez found her on the American Kennel Club Web site in 2003. “We hit it off,” she said. “We both like ethnic foods, and he wanted to learn about breeding.” Mr. Sanchez bred his dog with one of Ms. Barber’s, and talked with her often about the three puppies that were born, she said.

Ms. Barber said she took Mr. Sanchez to a dog show in San Francisco in 2004. He rented a tuxedo for the occasion.

The two had regular lunch dates at Thai, Indian and Brazilian restaurants for two years, until his work schedule made it difficult to meet. He had a big appetite, and it showed in the extra weight he carried on his 6-foot 2-inch frame.

His diet may have exacerbated his diabetes, Ms. Barber said. Last year Mr. Sanchez told her he had been put on medical leave by his employer, Connex Railroad, after his blood sugar tested at dangerous levels during a medical checkup.

Erica Swerdlow, a spokeswoman for Connex, said that “talking about his medical file is prohibited” by the ongoing investigation and confidentiality regulations.

Mr. Sanchez told Ms. Barber about his childhood on a small farm near Reno, Nev., where he lived with his parents, two brothers and a sister. It was where he learned to love animals and cattle, enrolling in 4-H.

Mr. Sanchez spoke little about the intervening years, said Ms. Barber, but public records show that he moved often, living in five states in the last 16 years. He worked as an engineer for the last 12 years, according to Tim Smith, the California chairman of the Brotherhood of Locomotive Engineers and Trainmen.

But a misdemeanor for shoplifting in 2002 may have suspended his work on the railroad for several months, said Wilson Wong, his former lawyer. Mr. Wong said Mr. Sanchez was arrested and convicted of one misdemeanor for stealing six Play Stations and two X-Boxes from a Costco in San Bernardino, near his Crestline home. Mr. Sanchez pleaded guilty to the charge, said Mr. Wong, and served 90 days in jail spread out over a few dozen weekends.

“He said he was diabetic, and Thanksgiving threw him off his schedule of eating and taking medication,” Mr. Wong said, “and he just wasn’t himself” when he stole the video game equipment.

“He was very remorseful,” the lawyer added.

Mr. Sanchez had been working for Amtrak when he was arrested, Mr. Wong said, but left that year and worked odd jobs while serving his sentence. Mr. Sanchez worked for Amtrak from 1998 to 2005, said Vernae Graham, an Amtrak spokeswoman, who would not confirm whether he worked consistently during that time.

At the time of the arrest, Mr. Sanchez was living with Mr. Burton in a middle-class neighborhood near forested mountains and a lake. Mr. Burton’s sister, Carolann Peschell, 46, said the couple seemed happy during the three years they spent together.

Mr. Burton was a waiter in Crestline, where the pair bought their house in 2000. Mr. Sanchez called Ms. Peschell regularly at her home in West Haven, Conn., she said, and made her laugh.

Relations between Ms. Peschell, her brother Charles Burton, 40, and Mr. Sanchez grew sour after Daniel Burton died on Feb. 14, 2003. The San Bernardino County coroner determined that Mr. Burton had hanged himself in the garage of the couple’s Crestline home, but his family would not accept that account.

Mr. Sanchez told a sheriff’s deputy that he had tried to break up with Mr. Burton the night before his partner’s suicide, and that Mr. Burton had threatened to stop making payments on the house, according to the coroner’s report.

In a Valentine’s Day card Mr. Burton left on a table in the house, Mr. Burton asked Mr. Sanchez to take care of their dog.

“I love you both very much,” Mr. Burton wrote.

Mr. Burton’s family suspected foul play but the coroner found nothing to support that assertion. The Burton family had not spoken with Mr. Sanchez for about four years, Charles Burton said.

The Burton siblings did speak to Mr. Sanchez’s mother, however, after their brother’s death. Mrs. Sanchez refused to discuss her son’s relationship with Daniel, said Charles Burton.

“Rob lived a very mysterious life,” Mr. Burton said. “His parents didn’t even know he was in a relationship with Dan. When we told his mother that Rob was gay, she said, ‘No way.’ She wouldn’t believe it.”

Ms. Barber, the dog breeder, said she suspected loneliness beneath the engineer’s jovial exterior.

“It wasn’t because of his personality, but because of his actions,” she said. “Rob tended to occupy a great deal of somebody’s time. He just wouldn’t leave.”

Mr. Sanchez worked a split schedule, driving the Metrolink train late at night and early in the morning with a four-hour break between shifts, said Mr. Smith, who described Mr. Sanchez as personable. But his schedule, he said, allowed little time for friends.

“When you whittle all that away, you’re lucky to get three hours of sleep,” he said. “Your circadian rhythms have just gone through the roof.”

Oliver Amelsberg, 83, lived next door to Mr. Sanchez in La Crescenta and spoke with him over his backyard fence, talking mainly of trains. “That’s about all he talked about,” Mr. Amelsberg said.

Almost two years ago, Mr. Sanchez built a taller fence with six-foot-tall wood boards, which hid him from view. “He turned out to be a very private man and quiet,” Mr. Amelsberg said.

Ms. Barber said long hours on the job might have given his neighbors the wrong impression.

“They might think he was a loner because he just wasn’t ever there,” she said.

Mr. Smith said Mr. Sanchez called regularly with concerns over safety issues, like broken or misplaced track flags. He said Mr. Sanchez had volunteered for training on safety regulations at a union conference in July.

“If he didn’t care about being safe, or was reckless,” Mr. Smith said, “he wouldn’t have come to that conference. He did care about safety, and I admire him for that.”

The National Transportation Safety Board said Mr. Sanchez sent text messages while on duty the day of the collision, though the exact times those messages were sent is still unknown. Within hours of the crash, KCBS-TV broadcast footage of teenage train buffs claiming that they had exchanged text messages with Mr. Sanchez moments before the collision.

Mr. Smith said “foamers,” a pejorative term for rail enthusiasts who linger along the tracks, photographing trains and waving at engineers, were a common sight on California railroads.

“Rob seemed to really enjoy being a railroad engineer,” he said. “If he was texting those teenagers, he’d have to have loved his job and wanted to share it with people. Someone who’s a malcontent is not going to reach out to those enthusiasts.”

Soon after the crash some rail buffs posted a video tribute on YouTube with footage taken the previous week. The video shows a smiling Mr. Sanchez along his route, driving the same locomotive and passenger cars that collided with the freight train.

“You take care, Rob,” said a message at the end of the tribute. “God speed and God bless you.”