A St. Martin Parish man killed his ex-girlfriend and her mother, torched their mobile home and stole two cars as he tried to escape before being captured near St. Francisville Saturday night, the state Fire Marshal’s Office said Sunday.

Firefighters discovered the bodies of Adeline Etienne, 68, and her daughter, Jamie James, 30, inside their burning mobile home at 1020 Whitney Drive, St. Martinville, about 3:30 p.m. Saturday, said Maj. Ginny Higgins, a St. Martin Parish Sheriff’s Office spokeswoman.

Investigators believe Dereke Ross Siner, 31, killed the women and then used gasoline to set the home on fire in an attempt to cover up evidence of the murders, said Deputy Chief Brant Thompson, of the state Fire Marshal’s Office, which is leading the investigation.

Thompson said firefighters managed to contain the fire and preserve much of the evidence inside the home, including the women’s bodies, a gasoline can and a handgun.

Witnesses told investigators they heard loud sounds coming from inside the trailer and saw Siner emerge from the burning mobile home, Thompson said.

Siner, who Thompson said is James’ ex-boyfriend and once lived at the Whitney Drive residence, drove away in James’ vehicle after lighting multiple fires throughout the home, Thompson said.

Siner parked James’ vehicle at his workplace in St. Martin Parish and drove away in his Chevrolet Tahoe, Thompson said.

Siner then crashed his Tahoe into the Vermilion River in neighboring Lafayette Parish, Thompson said. A passing motorist who saw the wreck and stopped to help wound up having her Chevrolet Impala stolen by Siner, Thompson said.

West Feliciana Parish sheriff’s deputies spotted Siner in the stolen car on La. 61 just south of St. Francisville at 5:26 p.m., said Erin Foster, West Feliciana Sheriff’s Office spokeswoman.

Siner led deputies and St. Francisville police on a high-speed chase that ended when he wrecked the stolen car about 10 miles away on Old Laurel Hill Road, Foster said.

Autopsies to determine the cause of death for James and Etienne are scheduled for Monday morning, but Thompson said both bodies “had obvious signs of blunt-force trauma.”

Thompson said it appeared James had ended the relationship “some time back,” but Siner told detectives he’d been persistent in trying to continue a relationship with her.

It wasn’t clear Sunday just how long their relationship lasted or when Siner moved out of the home, Thompson said.

Thompson said it appeared Siner had been living with relatives elsewhere in St. Martin Parish.

Siner is being held at the West Feliciana Parish Jail on two counts of first-degree murder, one count of aggravated arson and one count of obstruction of justice. Additional counts against him for stealing the car are expected in Lafayette Parish, Thompson said.

Foster said Siner is facing counts of aggravated flight from officers, illegal possession of stolen things and reckless operation of a vehicle in West Feliciana Parish.

Numerous pieces of evidence, including the three vehicles driven by Siner on Saturday, are being processed and analyzed at the State Police Crime Lab in Baton Rouge, Thompson said. Samples from the trailer will be tested to confirm whether gasoline or other chemicals were used to fuel the fire.

Thompson said Siner will be moved to the St. Martin Parish jail sometime this week.

Follow Bryn Stole on Twitter, @BrynStole.