Investigators believe missing pregnant military spouse may have been shot

Investigators believe the missing pregnant wife of a California-based Marine may have been shot while hunting with a married ex-Marine with whom she was having an affair.

The Desert Sun cited court documents that say on the day she disappeared three weeks ago, 20-year-old Erin Corwin had planned to meet with Christopher Brandon Lee to spend a "special day together" on a hunting trip.

A detective's affidavit shows the investigation is focusing on the 24-year-old Lee, who may have been the father of her child.

Lee said he was not with Corwin on the day she disappeared.

Authorities said Monday that Lee was arrested July 4 on suspicion of possession of a destructive device. He was released on bail.

Authorities wouldn't say if the two cases are connected.

Corwin, who is three months pregnant, was last last seen around 7 a.m. on June 28 at the Twentynine Palms home she shared with her husband, Lance Cpl. Jonathan Corwin. She was setting out to explore Joshua Tree National Park, her Marine husband told investigators with the San Bernardino County Sheriff’s Department.

According to court documents obtained by the newspaper, detectives believe the day trip was meant to celebrate Corwin's pregnancy, but that Lee was concerned his wife would learn of his affair.

"It is highly likely that Erin could have been harmed by an unknown firearm," investigators reportedly wrote in court documents. "Sometime after Erin left with Lee, her phone was deactivated (turned off). Detectives believe if Erin was injured and left at an undisclosed location, she would not (be) able to call for help."

Lee, who moved to Alaska last week, told authorities he was not with Corwin on the day she disappeared, but said he was out hunting in Joshua Tree National Park, according to the newspaper.

An affidavit filed by Detective Corey Emom states that text messages were sent by Erin Corwin to a friend, and Corwin indicated in the messages that she and Lee were in a romantic relationship and that they had planned a day trip on June 28.

Jonathan Corwin reported his wife missing the next day. Police located her 2013 Toyota Corolla in Twentynine Palms on June 30, but declined to say whether any potential evidence had been removed from the vehicle.

According to local media reports, Corwin told investigators his wife -- a volunteer horse rescue worker -- wanted to scout out the park in advance of a planned family visit. The Corwins are originally from Oak Ridge, Tenn., and Erin Corwin's mother had planned to visit her for her birthday in the coming weeks. Mother and daughter had already purchased tickets to visit SeaWorld, authorities said, and Erin Corwin had no known medical or psychological issues.

Corwin is described as 5 feet, 2 inches tall and 120 pounds with brown hair and blue eyes.

Anyone with information on her whereabouts it urged to call the San Bernardino County sheriff’s Specialized Investigation Division at (909) 387-3589 or sheriff’s dispatch at (909) 387-8313. Callers who wish to remain anonymous can contact the WeTip hotline at (800) 782-7463.

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FoxNews.com's Cristina Corbin and The Associated Press contributed to this report.