Authorities had not recovered the body of 20-year-old Lance Cpl. Maria Frances Lauterbach, but they believed she was buried in a shallow grave in a residential area of coastal Onslow County, Sheriff Ed Brown said.
The suspect, 21-year-old Cpl. Cesar Armando Lauren, has declined to meet with investigators and is not in custody, he said.
"They don't know where he is," Brown said of the suspect. "He's gone."
Lauterbach had claimed a superior had sexually assaulted her, and she was worried that the investigation was going nowhere, according to court documents. She vanished last month before she was to testify in a military probe.
Naval investigators said Friday the military was pursing rape charges against Lauren, and a hearing had been scheduled for December.
The court papers said the anticipated birth of the baby "might provide evidentiary credence to charges she lodged with military authorities that she was sexually assaulted by a senior military person."
Brown said detectives had tried to speak with Lauren, but he refused to do so, on the advice of his attorneys. Authorities said they didn't consider Lauren a flight risk until Friday, because they had information the pair carried on a "friendly relationship" after she reported the assault to military authorities.
The State Bureau of Investigation and the Marine Corps were assisting in the search for Lauren, who had not been charged with Lauterbach's death.
Lauterbach, originally from Dayton, Ohio, was reported missing Dec. 19 by her stepmother, who last spoke with her stepdaughter on Dec. 14, authorities said. Her cell phone was found Dec. 20 near the main gate at Camp Lejeune, and she missed a scheduled prenatal care appointment on Dec. 26.
Authorities found her vehicle at a bus station near the base on the Atlantic coast, and an employee there has told investigators it has been there since about the time of her disappearance. Brown said Friday she had purchased a bus ticket to El Paso, Texas, the day after she spoke with her stepmother, but the ticket has not been used.