After he fled to Mexico, Juan Marquez was detained while returning to the United States, police said.
TUSTIN, Calif. — A murder case that began with gunfire outside a Tustin workplace ended two days later at a border checkpoint, where federal officers detained the former boyfriend accused of killing Sandra Fernandez.
Authorities said Juan Marquez, 47, of Hawthorne, fled into Mexico after Fernandez, 42, of Anaheim, was shot near Yorba Street and Medford Avenue on May 14. Tustin police said detectives identified him as the suspect, obtained a warrant and worked with U.S. Customs and Border Protection before he was stopped May 16 as he tried to re-enter the United States. He is being held without bail in Orange County Jail on a murder charge.
The border arrest became a key turn in the case because police said Marquez had crossed south through the San Ysidro Port of Entry after the killing. Investigators did not say where he went in Mexico or why he returned so soon. They did say he was detained on the warrant when he came back through the checkpoint. Tustin detectives then took custody of him and booked him into jail. The arrest closed the first phase of a search that began less than 48 hours earlier, after witnesses reported a man in black fleeing the scene in a dark, older-model sedan.
The shooting was reported shortly after 6 p.m. Thursday at an intersection lined with traffic, businesses and parking areas. Officers arrived and found Fernandez unresponsive, suffering from gunshot wounds. She was pronounced dead at the scene. Police said their investigation showed Marquez, a former boyfriend, had laid in wait near her workplace and killed her after she left for home. Family members said Fernandez had been leaving a training session tied to a new job. One local report said she was shot near her car, which had been parked off-site. Police have not publicly released the exact number of shots fired.
After the arrest, prosecutors filed a murder charge and added a special circumstance allegation of lying in wait. They also added an enhancement alleging discharge of a gun causing death. Those filings point to the theory prosecutors expect to present: that the attack was planned and carried out with a firearm. The allegations do not decide guilt, which would be determined in court. A court date was not immediately available in early public reports after the arrest and filing. Authorities also have not announced whether Marquez had an attorney or entered a plea.
Fernandez’s death drew public grief from relatives who said she was still building a better path for her children. A family fundraiser said she had three children: a 5-year-old, a 14-year-old and an older son finishing college. The page said she was a single mother who worked to provide for her family and had only recently started her job in the area. The organizer, Melitza Uribe, said funds were intended for funeral and burial expenses and would be paid toward arrangements. The family also planned a May 24 kermes to help raise money for services.
Relatives said the arrest did not answer their deepest question. Uribe said Fernandez was known for joy, care and a strong presence in the family. “There’s so much you can see from the outside,” Uribe said, describing Fernandez’s happiness, helping hands and devotion as a mother. She said the family was left with a void and no clear explanation. “We don’t know the motive. We don’t know why,” Uribe said. Police have not disclosed a motive, and they have not said whether they found any message, argument or prior report that explained the shooting.
The location of the arrest also added a regional layer to the case. San Ysidro is one of the busiest land border crossings in the country, linking San Diego and Tijuana. Police said Marquez crossed there after the killing and was detained there on his return. The timeline suggests investigators moved quickly to identify him, seek a warrant and share information with federal officers. Still, several parts of the investigation remain public unknowns, including whether detectives recovered the dark sedan, whether surveillance video captured the shooting or escape, and whether the firearm was found.
Coworkers said Fernandez had only begun to settle into the new workplace. Cassie Rossel said Fernandez had already made relationships and had a strong impact in less than a month. That short span became part of how people around her described the loss: a mother at the start of a job, leaving a training session, killed before she reached home. Police said the shooting appeared isolated and that there was no continuing threat to the public, but the case left a public corner in Tustin tied to a homicide investigation and a family funeral.
Prosecutors have charged him with murder and are pursuing the lying-in-wait allegation. Investigators have not announced a motive, and Fernandez’s family continues to await answers about the moments before the shooting. At the moment, Marquez remains jailed without bail while the murder case moves toward its next court setting.
Author note: Last updated June 17, 2026.