08/26/2014 AT 08:30 PM EDT
08/26/2014 AT 06:55 PM EDT
Christopher Brandon Lee, the man accused of murdering his alleged lover Erin Corwin
, pleaded not guilty Tuesday to first-degree murder with a special allegation of lying in wait.
Police believe that Lee, a neighbor of Corwin and her Marine husband, Jon, killed the 19-year-old and stashed her body near the Joshua Tree National Park after she vanished on June 28.
Her body was eventually located
deep within a remote gold mine shaft on Aug. 17.
The cave specialist instrumental in locating Corwin's body is still scratching his head over the San Bernardino Sheriff's Department's success in finding the teenage murder victim.
"I kept telling them, 'She's not in a mine shaft. Who's going to dump a body in a mineshaft in 2014? This isn't a movie,' " says Doug Billings, who was called in to assist in the search when detectives learned of his extensive knowledge of the hundreds of old mines near the rugged national park.
"They just kept saying, 'She's in a shaft somewhere and you're going to find her,' " says Billings, who started exploring the 130-year-old mines around the park as a teenager. "She just happened to go missing in an area that I'd spent 30 years searching. I knew every canyon, trail, mine shaft and road in that area."
Working with evidence provided by detectives, Billings went through his old notes, studied satellite photos and put together a list of possible locations where Corwin's body might be found.
For the next six weeks, dozens of volunteers from caving clubs throughout southern California looked alongside search and rescue crews and braved 117-degree heat while searching 85 different shafts identified by Billings.
Corwin's body was eventually found in a 140-foot deep mine.
"This particular mine was number two on my list," recalls Billings. "I was standing 50 feet from it on our second day out, but the temperatures were so bad that we had to leave because the dogs couldn't handle the heat."
Detectives also located .22-caliber cartridge casings and pieces of rebar near Corwin's body that matched those found in Lee's Jeep.
Lee, a former Marine who The Desert Sun
reports pleaded not guilty on Tuesday, is being held without bail in a San Bernardino County jail after being extradited from Alaska.
Jon Corwin attended Lee's arraignment hearing, sitting in the back of the room with his father, Tom, according to the newspaper. Lee has another court hearing scheduled Sept. 16.