CONCORD (CBS SF) — Contra Costa County Fire Protection District announced Monday the arrests of two arson suspects in unrelated vehicle fires that occurred in Antioch and Martinez late last week.

Fire officials said Lisa St. Onge, 39, was being held on one count of arson while Milan Popich, 39, was in county jail on two counts of arson.

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According to investigators, the first fire and ensuing arrest occurred in Antioch Thursday morning and the second took place later in the early evening hours in Martinez.

“Quick work of our fire investigators in close partnership with local law enforcement agencies has resulted in the removal of two dangerous arsonists from our streets,” said Fire Chief Lewis T. Broschard III, Contra Costa County Fire Protection District.

On Aug. 20 at approximately 10 a.m., an fire investigators responded to a vehicle blaze on Auto Center Drive in Antioch. Examining the fire scene and surveillance video, the fire was determined to be intentionally set. Soon thereafter, Antioch Police found the suspect vehicle in Antioch, detaining four subjects.

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After interviewing those detained, St. Onge, 39, was arrested.

Later that day, at approximately 6:30 p.m., an arson investigator again responded to a report of vehicle fires on the shoulder of westbound Highway 4 in Martinez.

On scene, California Highway Patrol officers had detained Popich from one of the two vehicles burned. After investigation of both vehicles, the fires were determined to have been purposefully set. Popich was the arrested for arson.

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Both suspects have been booked into the Contra Costa County Detention Facility in Martinez where they remain in custody. Both cases will be presented to the District Attorney’s Office for a decision early next week.