A 19-year-old illegal immigrant from El Salvador is accused of fatally stabbing a female co-worker he had an “intimate relationship” with — then dousing her body in gasoline near a Virginia trail.

Alexis Antonio Cedillos-Campos was arrested Wednesday for killing 42-year-old Carmen Lizet Puch, who was described as a “loving mother of a 3-year-old girl,” Fairfax County Police Chief Kevin Davis announced at a press conference.

Puch was found stabbed multiple times and drenched in gasoline in the parking lot of Difficult Run Park in Great Falls, about 15 miles outside Washington, DC, on Monday.

Davis said investigators found that Cedillos-Campos and Puch worked together at Bitez restaurant — a Halal-focused eatery in Herndon, Va. — and determined the two had been in an “intimate relationship” before the killing.

Detectives are still working to understand the full picture — including whether other relationships may have contributed to the motive.

“We also know that our killer left the restaurant on the night of the murder with a fixed-blade knife that he took from the restaurant,” Davis said, adding that Cedillos-Campos also took a pair of latex gloves and a water bottle from the establishment.

“We have video footage of our suspect at the restaurant where he worked with our victim, arming himself with a fixed blade knife, taking a pair of black latex gloves, taking a water bottle, and then off he goes with the intent to do harm and kill the victim.”

Davis said that Cedillos-Campos siphoned gas from a motorcycle and filled the water bottle in a failed attempt to set her body on fire after stabbing her “repeatedly.”

“The way that she was treated by this killer was reprehensible,” Davis said.

Police said a jogger called 911 after finding Puch lying next to her 2011 Honda Civic in a small gravel parking lot near the trail at around 6:45 a.m.