Job Supervisor Slain at Firm in San Marcos : Violence: Subordinate at manufacturing plant arrested. Investigators say they know of no motive for the shooting.

A 22-year-old man allegedly shot and killed his supervisor during a work break Wednesday morning in a parking lot outside a San Marcos manufacturing firm, sheriff’s spokesmen said.

Jose Luis Maldonado of Oceanside was arrested for purportedly gunning down his boss before a dozen witnesses at Professional Care Products Inc., in an industrial complex about a mile south of California 78.

The medical examiner’s office identified the victim as Juan Lopez-Rodriguez, a 29-year-old Pro-Care employee.

The shooting comes less than a week after a fired employee of General Dynamics in San Diego shot two co-workers in the back of the head on Friday, killing one and critically injuring the other.

Executives of Pro-Care, a firm that manufactures orthopedic devices, said that they knew of no work-related disagreements between the two men.

Sheriff’s Lt. John Tenwolde said investigators have no idea why Maldonado, described by friends and family as a happy-go-lucky man who liked to toss a football with his younger brother, pulled a semi-automatic handgun from his waistband and fired “more than once” at his boss, killing him instantly.

“It’s absolutely senseless on the basis of what we know at this time. We don’t know why it happened. (The company is) unaware of any dispute that existed between these two men,” Tenwolde said.

Witnesses said that before the shooting at 10:15 a.m., there had been no argument or scuffling between Maldonado and Lopez, who had recently been promoted to assistant supervisor in the packaging department.

Martha Lopez, wife of the slain man, learned of her husband’s death shortly after 6 p.m. when friends and his co-workers visited their South Escondido home to console the family.

Lopez had lived in Escondido for about a year with Martha and their 9-year-old twins, a boy and a girl.

Jose Luis Vallon, Lopez’s stepson, said his stepfather had spoken disparagingly of Maldonado in the past, calling him a “crazy guy who was usually . . . out of control.” Lopez also voiced suspicions that Maldonado had drug problems, Vallon said.

Other co-workers said that Maldonado had told them he used drugs in the past but that “he said he had quit” before coming to work at Pro-Care.

Sheriff’s deputies gave this chronology of the shooting:

The workers went on their usual morning break at 10 a.m., Lopez chatting with a group of co-workers in the parking lot behind the building in the 1700 block of La Costa Meadows Drive, Tenwolde said.

“Then, break time was over and employees were beginning to file back inside. And then, suddenly, one employee pulled a gun and fired,” Tenwolde said.

When a sheriff’s deputy arrived on the scene, Maldonado was sitting with his sister, who works at the same company, in a patio area near the shooting scene, the brown-handled gun lying on top of a garbage bin, Tenwolde said.

Sheriff’s deputies took both Maldonado and his sister into custody. She was released several hours later.

Company executives said Maldonado had worked for the firm for 10 months, while Lopez had been part of the organization for nearly two years. Pro-Care makes knee braces, neck braces and other orthopedic devices.

“He was a very nice gentleman,” Pro-Care president Greg Stetman said of Lopez. “There’s absolutely no reason that we know of as to why this happened.”

Investigators found two bullet casings about 15 feet from where Lopez lay face down, his arms beneath him as if clutching his chest, a half-empty soda bottle lying near his head and his burgundy-and-silver van a few yards away.

On Wednesday afternoon, Maldonado’s family and friends in his far northeast Oceanside neighborhood expressed shock over the shooting, saying the man who pulled the trigger of a semi-automatic handgun hours earlier surely was not the young man they knew.

“He was a friendly guy, everyone in the neighborhood liked him,” said Isabel Maldonado, 23, the suspect’s sister. “This is just . . . we don’t know what happened.”

Isabel Maldonado said her brother, Jose, lived at home with his parents, his 4-year-old sister Candace, and 13-year-old brother Alex. Two other sisters and a brother have moved out of the house.

“I just talked with my brother the other day and he never said anything about any problems at work,” she said, standing in the doorway of her home, holding her 5-month-old daughter in her arms.

“He’s an easygoing guy. Usually, he would come home from work, go to his room and listen to music. After dinner, he would just sit and watch television. Even on weekends, he didn’t go out. He just stayed at home and watched television.”

On Wednesday, several of Maldonado’s relatives gathered at the home on Arthur Avenue where the family has lived for 20 years. Isabel Maldonado said her parents were still too shaken to talk to reporters.

“My mother told me he didn’t say anything to her (Tuesday night) about any troubles at work,” she said. “He just told my mom he was hungry.”

When asked if she knew about any disagreements her brother might have had with co-workers, she replied: “I don’t know. But this guy must have been bugging him.”

Zeke Gonzalez, 20, who attended grammar school with Maldonado, called him a quiet kid who never got into any trouble.

“We grew up together,” said Gonzalez, who lives across the street from Maldonado. “He was smooth, man. In all the years in school, I never saw him get mad once.”

Friends said Maldonado attended Del Rio Elementary School and Lincoln Junior High School before graduating from El Camino High about four years ago.

“He’s cool people, but he didn’t really hang out much with the guys in the neighborhood,” said neighbor George Cruz. “He kept to himself. Once in awhile, I saw him on the street with his kid brother. He never ran with any gang, like some guys do.”

Heidi Hunt, 20, who lives across the street from Maldonado, described him as a thin man with dark hair who was starting to grow a goatee.

“He was just such a down-to-earth guy,” she said. “I’ve seen so many other guys in this neighborhood high (on drugs) before, but never Jose.

“This whole thing is so unbelievable. I don’t care how many people said they saw Jose fire that gun, I don’t believe it, not the Jose that I know around this neighborhood.”

Times staff writers John M. Glionna and Nancy Ray contributed to this story.