JACKSONVILLE, North Carolina (CNN) -- Police believe they have found the remains of a missing Marine buried in the backyard of the prime suspect in the case and blood spatter evidence inside his home, authorities said Friday evening.

Investigators search for the body of Lance Cpl. Maria Lauterbach Friday.

Tests found the "trace of violent activity in the house" and "evidence of an attempted cleanup," said Onslow County Sheriff Ed Brown.

Investigators are treating the death of Lance Cpl. Maria Lauterbach as a murder, Brown added.

Lauterbach, 20 -- who was eight months pregnant -- was reported missing from Camp Lejeune, North Carolina, by her mother December 19.

Cpl. Cesar Armando Laurean, whom Lauterbach had accused of rape, is the suspected killer, and is being sought, Brown said.

He confirmed that Laurean had left a note, but did not divulge what it said.

Investigators told CNN, however, that Laurean left a note to his wife saying Lauterbach had committed suicide and that he buried the body.

"Evidence now is saying what he's claiming happened did not happen like he said it happened," Brown said.

Authorities searching Laurean's home found a cavity in his backyard earlier Friday.

A preliminary investigation indicated a "suspicious situation," prompting police to secure the scene and wait for daylight Saturday. Watch authorities search for a grave »

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"We think that we have found what would be the skeletal remains [of Lauterbach]," Onslow County District Attorney Dewey Hudson told reporters.

While authorities will not know for sure until Saturday, "there are certainly some strong indicators that there are human remains" buried in the cavity, he said.

"It doesn't take a rocket scientist to understand if there's a cavity out back and blood on the inside, that's probably going to be a key location for where this crime may have taken place," Brown said.

He also hinted that investigators have uncovered more twists in the case.

"I do think this case is going to be a bizarre ending, and when I say bizarre, more than just a death and a burial."

Brown stunned reporters earlier in the day by opening a press conference with the announcement: "She is dead, and she is buried." Watch Brown describe the cavity »

Laurean, a 21-year-old from Nevada, is believed to have left the Marine base about 4 a.m. Friday, driving a black Dodge pickup with North Carolina license plate TRR1522, Brown said.

He repeatedly refused to meet with investigators, finally telling them that his attorney wouldn't let him.

The sheriff was downcast at a midday news conference.

"These cases, investigations, become personal. I just want to cry," he said. "I'm telling you, at this point, I'm down, way down." Watch sheriff announce that Marine is dead »

Mary Lauterbach reported her daughter missing after being unable to contact her. She said she last spoke to her December 14.

In a handwritten note, the Lauterbach family in Vandalia, Ohio, mourned their loss.

"We would like to thank everyone for their prayers in this time of grieving," the note said. "Maria has been a gift for her family and friends. The outpouring of love from family, friends, neighbors and the general community has been very touching.

"Please understand that the family needs time alone to deal with this tragedy. We wish to thank everyone for their love and concern."

"They're having a very difficult time dealing with this," said Peter Steiner, a Kentucky psychiatrist who is Maria Lauterbach's uncle and Mary Lauterbach's brother. "They remained hopeful, and really, although everyone knew it was a possibility, it was very difficult when it became apparent."

Brown said a witness came forward Friday morning with a statement and evidence that convinced authorities Lauterbach was dead. Brown wouldn't name the witness, or describe Lauterbach's cause of death, except to say she died "from an injury."

Asked whether the witness was in protective custody, Brown said the person does not feel the need for protective custody, as Laurean likely left the county and possibly the state.

A source close to the investigation told CNN the witness is Laurean's wife.

Lauterbach's relatives believe the pregnancy was the result of the alleged rape, Steiner said.

A reporter who asked military officials why Laurean hadn't been taken into custody after Lauterbach reported the alleged rape was told there were indications that Lauterbach and Laurean carried on "some sort of friendly relationship" after she filed the complaint against him.

"The information developed over the last 24 hours leads us to believe that she still had some kind of contact" with him, said Paul Ciccarelli, agent in charge of the Naval Criminal Investigative Service at Camp Lejeune.

Because of that, Laurean wasn't considered a flight risk, he said.

Steiner disputed that, saying his niece had no relationship with Laurean.

Ciccarelli also said the rape investigation is still active. Watch police face unanswered questions »

Lauterbach disappeared before she was able to testify at an Article 32 hearing -- a kind of military grand jury -- about the sexual assault.

Earlier Friday, Brown said a Marine who returned to North Carolina from California -- Sgt. Daniel Durham, 20, in whose home Lauterbach had been living for a short time -- was questioned, but does not appear to have any link to the death.

Lauterbach had rented a room in Durham's home, off the base, because she had been subjected to repeated harassment by the Marines after reporting the alleged rape, Steiner said. Her car had been keyed and an anonymous person had "slugged" her in the face, he said.

Lauterbach's cell phone was found on a roadside near Camp Lejeune on December 20. Her car was found Monday in the parking lot of a fast-food restaurant and had apparently been there since December 15, Brown said.

A bus ticket to El Paso, Texas, was bought in Lauterbach's name on the same day, but Brown said it was never used. See a timeline of the case »

Investigators have said a withdrawal from Lauterbach's bank account was made on December 14, and there was "suspicious activity" on the account 10 days later.

Lauterbach and her mother last spoke about 2:30 p.m. the day Lauterbach disappeared, Steiner said. At the time, she had experienced some contractions. "She was ready to have that baby."

His niece "was an energetic, very athletic, beautiful young lady. She was a person that we're all dearly, dearly going to miss," he said. E-mail to a friend

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