Brittany Killgore was hoping to unwind for three days after filing for divorce from her Marine husband serving in Afghanistan.
Prosecutors believe things quickly went wrong when she met another Marine for a night out.
"She sent a text saying, `Help,'" Patrick Espinoza, a deputy district attorney in San Diego County, said Thursday. "She was missing from that point on."
Authorities said Killgore's body was found in brush near Lake Skinner on April 17, hours after paramedics were called to a San Diego motel and found another woman with self-inflicted cuts and a suicide note.
Killgore's message to an unidentified friend was disclosed at an arraignment for Louis Ray Perez, 45, who pleaded not guilty to murder.
The brief hearing offered the most details yet of what authorities believe happened to the 22-year-old Killgore after she disappeared on April 13.
Espinoza said investigators found Killgore's blood and a weapon in Perez's car. He also said Perez told investigators he dropped off Killgore in downtown San Diego's bustling Gaslamp District, but investigators concluded that he lied about his whereabouts and stayed about 60 miles north in Fallbrook, where Killgore lived.
Jessica Lynn Lopez, 25, the woman authorities said was found by paramedics at the motel, also has pleaded not guilty to murder.
The prosecutor said Lopez and Perez once lived together but didn't indicate when or where. Lopez currently lives a mile from Killgore's second-floor apartment overlooking Camp Pendleton.
Espinoza didn't disclose a possible motive or other details about the death during the hearing, and he later declined to elaborate on the investigation.
It's still unclear how Killgore died and whether the unspecified weapon authorities said they found in Perez's car was used in the killing.
Perez's attorney, Jeff Reichert, said Lopez's suicide note shows "very, very clearly" that she killed Killgore and that his client was not involved.
"The court has information in its hands that exonerates my client on this charge," Reichert said.
However, details of the note were not released, and Superior Court Judge Kimberlee Lagotta ordered it to be sealed.
Perez, a Marine for 16 years who is married and has lived in the San Diego area for 10 years, has also pleaded not guilty to stealing an assault weapon. The prosecutor said Perez stole the weapon and a motorcycle from a trailer at Camp Pendleton.
The death has shaken many at Camp Pendleton and neighboring Fallbrook, known for its rolling hills and avocado orchards. The Killgores lived in one of several apartment complexes on Ammunition Road that advertise special rates for military members and is close to a base entrance.
Killgore recently separated from Marine Lance Cpl. Cory Killgore, who was in Afghanistan when she disappeared. She cited irreconcilable differences in her divorce filing but gave no other details.
Cory Killgore made his first public comments about his wife's death in a statement released Thursday by the San Diego County Sheriff's Department.
"My wife Brittany was beautiful beyond words and her murder has left me devastated," the statement said. "My duty to her memory is now to ensure her good reputation remains intact, and help law enforcement and prosecutors secure justice for the person or persons who took her away from me."
Cory Killgore has not been named as a suspect or person of interest in the killing. The couple married in July 2010.
The judge set bail at $3 million each for Perez and Lopez and scheduled a preliminary hearing for May 30. If convicted, they could face maximum sentences of life in prison.