Erin Corwin Murder: Suspected Killer Admits He Searched for 'How to Dispose' of Body
08/23/2014 AT 03:00 PM EDT
The revelation is just part of the evidence that San Bernardino County prosecutors have amassed against Lee, 24, who police contend was having an affair with Corwin and killed her out of fear his wife would learn of the relationship.
Several days before her disappearance, Corwin, 19, told a friend that she and Lee were planning on taking a "special" trip together, according to court documents.
An additional murder charge might be filed against Lee pending the outcome of Corwin's autopsy, which won't be finalized for the next four to six weeks.
"There's still an ongoing investigation to determine if she was pregnant at the time of the murder," San Bernardino District Attorney Michael Ramos tells PEOPLE. "If we find that to be true and the fetus was far enough along, there could be another kind of murder charge filed."
Corwin's body was located at the bottom of a 125-foot gold-mine shaft on Sunday, seven weeks after her husband, Marine Cpl. Jon Corwin, reported her missing. Detectives also discovered .22-caliber casings and pieces of rebar at the mine shaft that matched those found in Lee's Jeep.
Lee, who is awaiting extradition from Alaska, where he recently moved with his wife and daughter, told police he was "collecting tires" on the morning Corwin disappeared. Detectives found a tire at the mine shaft. A witness also informed investigators that Lee asked him "the best way to dispose of a human body," according to court documents.
The authorities are also curious to learn whether Lee's wife, Nichole, may have played a role in the murder.
"Investigators would like to interview her at some point," says Cynthia Bachman with the San Bernardino County Sheriff's Department, "to determine her involvement, if any."
Prosecutors are still "a couple months" away from deciding whether or not they'll ask for the death penalty for Lee, added Ramos.
"I was only able to speak with him briefly the day before he waived extradition," Lee's lawyer David Kaloyanides told The Desert Sun. "He's not pleased that the case has gone in this direction, but seems to be doing okay."