Editor's Note: This story is developing. Information will be added as it is received.
UPDATE 5 p.m. April 18: Body confirmed as that of Brittany Killgore.
UPDATE 9:30 p.m. April 17:
A body believed to be that of Brittany Killgore was found near Murrieta, according to police officials.
A maintenance worker found the remains around 2:30 p.m. today about a mile west of Lake Skinner on the side of Borel Road, according to Lt. Larry Nesbit of the San Diego Sheriff's Department.
"A road worker who was mowing the shoulder of the road made the discovery," Nesbit said.
Law enforcement and a police helicopter swarmed the area, taking residents of the rural area by surprise.
"We just saw all these police cars and helicopters," said Bonnie Monier, whose home stands a few hundred feet away from the place the body was found. "I don't think anybody around here saw anything (before law enforcement arrived)."
Deputies talked to the worker shortly before the discovery and asked him to keep his eyes open. "The body was not readily visible from the roadway," Nesbit said.
He declined to release the suspected cause of death.
Investigators searching for a missing 22-year-old North San Diego County woman who disappeared last week under suspicious circumstances found a body today east of Murrieta and arrested a 27-year-old woman on suspicion of murder.
The discovery of the body off Warren Road, near Lake Skinner in southwest Riverside County, was made about 2:30 p.m., San Diego County Sheriff's Department Capt. Duncan Fraser said. It was not immediately clear if the body was that of Brittany Killgore of Fallbrook, who went missing Friday, he said.
Meanwhile, detectives made a second arrest in the case today, according to Fraser. Jessica Lynn Lopez, 27, was taken into custody at a motel on Rosecrans Street in San Diego and was expected to be booked on suspicion of murder.
On Sunday, detectives arrested a Camp Pendleton Marine, Louis Ray Perez, 45, who they believe was with Killgore just before she went missing. Perez was booked on an unrelated weapon charge, though he "is being actively investigated for this disappearance," Fraser told reporters.
Borel Road near Lake Skinner was closed today around 1:30 p.m. due to a search operation between the Riverside and San Diego counties' sheriff's department.
Neither San Diego nor Riverside County sheriff's spokespeople were able to say whether they were searching for Killgore, whose estranged husband, Cory, was deployed on combat duty in Afghanistan but on his way back. Killgore had filed for divorce last week, court records indicate.
Investigators went to the area where the body was found "based on leads stemming from the arrest of Lopez," Fraser said during a late-afternoon briefing. The captain told reporters he could release very limited information about the case before heading north to the spot where the dead woman turned up.
"I can't comment on the condition of the body that was found," he said. "We have not confirmed that the body ... is that of Brittany Killgore. ... The medical examiner will make that confirmation."
Killgore was last seen at 5 p.m. Friday in Fallbrook. A 5-foot-7-inch, roughly 130-pound brunette with brown eyes, Killgore was wearing a dark-purple evening gown with shiny floral patterns on it at the time of her disappearance.
Investigators believed there was foul play involved, and at first focused their search efforts in the De Luz Canyon area, southwest of Murrieta near the Riverside-San Diego counties line.
Killgore's cellphone was found in the San Diego Gaslamp Quarter, though investigators told news crews they did not believe she'd gone there herself the night she vanished.
After being questioned about Killgore, Perez was arrested on suspicion of possessing a stolen AR-15 military assault rifle. He was being held at San Diego Central Jail on $500,000 bail pending arraignment, scheduled for Wednesday afternoon.
Sheriff's Lt. Larry Nesbit said Perez had been "uncooperative and not completely forthcoming about his knowledge." The lieutenant would not comment on the nature of the missing woman's relationship with the serviceman.
—Peter Surowski contributed to this report.