Missing Marine Wife May Have Been Having Affair With Neighbor

— -- Authorities are investigating the possibility that a missing California woman – the wife of a Marine – was having an affair with her married neighbor and was pregnant with his child, according to a search warrant.

Erin Corwin, 20, has not been seen since June 28, vanishing from the city of Twentynine Palms without a trace. Investigators say her husband, Lance Cpl. Jonathan Corwin, reported her missing one day after she was last seen leaving for Joshua Tree National Park in southeastern California.

Her Toyota Corolla was found not far from the military base where her husband is stationed.

Search Intensifies for Marine's Missing Pregnant Wife

Mystery Deepens in Case of Missing Pregnant Woman Erin Corwin

Authorities say the circumstances surrounding Corwin’s disappearance are suspicious.

“At this point we’re trying to investigate each and every person who has been an acquaintance with Erin,” San Bernardino County Sheriff Randy Naquin said.

That includes Christopher Lee, a Marine rifleman who was recently honorably discharged. According to the search warrant, Lee initially denied knowing Corwin well, but investigators say Corwin’s friend told them she might have been pregnant with Lee’s child.

Additionally, Lee was worried that his wife would divorce him and keep him from his child with her if she found out about the affair and pregnancy, the friend said, according to the search warrant. It's unclear who and what the warrant targets.

Lee, 24, says he went hunting in the national park the same day Corwin told her husband she was going there, according to the search warrant. But Lee has said he denied seeing her that day.

Investigators are searching the park for clues.

“We’re looking for a crime scene,” Naquin said. “We're looking for something that is going to give us an indication that something has or has not happened to her.”

Lee has not been named a person of interest or suspect. ABC News has been unable to reach him.

Police have not ruled out the possibility that Corwin may be voluntarily missing, but, at this point, her whereabouts remain a mystery.

“It is highly likely that Erin could have been harmed by an unknown firearm,” police said in the search warrant.

Lee was arrested July 4 on an unrelated weapons charge for possessing a destructive device and is reportedly out on bail.

ABC News Chief Legal Affairs Anchor Dan Abrams said authorities will continue to focus on Lee, but need to definitively prove that a crime occurred.

“In a situation like this, where a woman who disappeared was possibly having an affair, you look first at two people: the husband and the boyfriend,” Abrams said. “As of now, it doesn’t seem the authorities are considering the husband as a person of interest.

“It’s clear they now suspect very strongly there was foul play. And as time passes, it will become clearer and clearer that a crime was committed.”