They were neighbors in a housing complex for junior enlisted Marines at the desert base at Twentynine Palms.
The husband in one couple and the wife in the other shared a passion for horses. They volunteered at a horse rescue facility in nearby Yucca Valley.
Then Erin Corwin, 19, who was three months pregnant, disappeared June 28. At first, Marine and San Bernardino County investigators were unsure whether she had met foul play or had fled her marriage.
But within weeks, suspicion focused on Christopher Lee, 24, a neighbor and fellow volunteer at the White Rock Horse Rescue. Lee and Corwin had been having an affair, investigators discovered.
On Saturday night, after seven weeks of searching the desert and following fruitless leads, a body was found at the bottom of an abandoned, 140-foot mine shaft southeast of Twentynine Palms.
By Sunday night, the body had been recovered and dental records confirmed that it was Corwin's.
Half an hour later, Lee was arrested in Anchorage by local police and FBI agents, apparently without incident.
Lee may have been afraid that Corwin would tell his wife that she was pregnant with his child, according to a search warrant affidavit.
"At this point, all indications" point to it being filed as a murder case, San Bernardino County Dist. Atty. Mike Ramos said at a news conference Monday. Sheriff John McMahon said more arrests are possible.
On the day she disappeared, Corwin had told her husband, Cpl. Jonathan Corwin, that she wanted to scout locations in Joshua Tree National Park that she could show to her mother during an upcoming visit from Tennessee. Her abandoned Toyota Corolla was found two days later near the base.
"She's really young, really innocent," her sister-in-law, DeeAnna Heavilin, told The Times as the search continued. "She's just a kind-hearted, trusting, sweet, sweet soul."
As hundreds of searchers scoured the desert for clues to Corwin's disappearance, Lee was discharged from the Marine Corps and prepared to move to his home state of Alaska with his wife, Nicole, and their daughter.
According to a search warrant issued in late July, Nicole Lee told a friend that her husband had said Corwin's body would never be found.
Based on the July warrant, the Lees' apartment was searched and Lee was arrested on suspicion of possessing a destructive device. He posted bail and moved to Alaska days later.
Investigators declined to say how Corwin was killed. But in the July search warrant in which the alleged affair was first mentioned, investigators speculated that she had been shot.
During the search of the apartment in July, Lee admitted being romantically attracted to Corwin but denied that they had had sex. He said that the day she disappeared they had planned to go hunting but that he had gone alone. Investigators identified tire prints next to Corwin's car that matched Lee's Jeep.
Just how investigators found the body in an area of rugged terrain and hundreds of mine shafts remains unclear. Investigators said only that they had developed information from interviews, cellphones and other electronic devices.
"It is not a very easily accessible area; it is very rough terrain out there," Sheriff's Sgt. Trevis Newport said. "One would have a difficult time even in a four-wheel-drive vehicle. It is a very dangerous area. There are lots of mine pits out there. And it's very remote."
On Saturday, search teams focused on the areas of Rose of Peru Mining District, Brooklyn Mining District and Los Angeles Mining District in a desolate area controlled by the Bureau of Land Management. A body was spotted with a camera lowered into a shaft.
After the body was located Saturday evening, the depth of the mine shaft and its noxious air hindered recovery efforts. A firefighter suffered heart problems and was hit by a falling rock.
With help from the San Bernardino County Urban Search and Rescue Team, the body was recovered by Sunday evening.
Corwin was living far from her family for the first time. Before she and her husband moved to Twentynine Palms, she had never lived more than a mile from her parents in Oak Ridge, Tenn., her sister-in-law told the Riverside Press-Enterprise.
Her mother was coming to visit to celebrate her daughter's 20th birthday. They planned to visit the San Diego Zoo and SeaWorld. The family thought Erin might have gotten lost on her way to SeaWorld.
While her husband was at work, Corwin spent numerous hours with the horses at White Rock Horse Rescue, adopting an 8-year-old quarter horse named Casey.
After Monday's news conference, Corwin's family posted a statement on Facebook thanking law enforcement personnel and asking the media to respect the family's privacy.
"Though we were praying for a different outcome, we are relieved to have this part of the investigation behind us and to be able to begin mourning the loss of our sweet girl," the statement said. "Please continue to pray for our family and that justice will be found for Erin."
Times staff writer Tony Perry in San Diego contributed to this report.