Police in Erin Corwin probe can't rule out Marine's wife 'voluntarily missing'

While California authorities strongly suspect foul play in the disappearance of 20-year-old Erin Corwin, investigators say they can't rule out the pregnant military spouse "could be voluntarily missing."

"We are looking for a crime scene," Leland Boldt, captain of the San Bernardino County Sheriff’s Specialized Investigation Division, said Tuesday.

The statement, part of a press release by the sheriff's department, added: "Although suspicious circumstances have existed from the inception of this investigation there is still not enough evidence to rule out that Erin Corwin could be voluntarily missing."

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 Desert Sun newspaper, detectives believe the day trip was meant to celebrate Corwin's pregnancy by another man -- 24-year-old Christopher Brandon Lee -- with whom they believe she was having an affair.

Lee, who was arrested July 4 on suspicion of possession of a destructive device and later released, claims he was not with Corwin on the day she disappeared -- though he confirmed he was hunting June 28 in Joshua Tree National Park, according to court documents cited by the newspaper. Lee moved to Alaska last week.

Investigators also reportedly wrote in documents that Corwin may have been shot while hunting with Lee, a married ex-Marine, in what was intended to be a "special day together" on a hunting trip.

"It is highly likely that Erin could have been harmed by an unknown firearm," detectives 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."

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, according to the newspaper.

KTLA-TV reported Tuesday that a police affidavit also alleges that Lee's wife told a friend, "that without a body the detectives did not have a case against them and the detectives would never find the body."

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.

On Tuesday, detectives said they received information about "possible locations to be searched for potential evidence of foul play" regarding Corwin's disappearance.

"It is imperative investigators determine whether or not there was foul play," Sgt. Trevis Newport said. "Search warrants have been executed as part of this investigation to assist investigators in determining what may have occurred."

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.

FoxNews.com's Cristina Corbin contributed to this report.