A West Virginia man was arrested for allegedly killing his girlfriend's teenage daughter, police said Thursday, the same day a decomposing body believed to be the girl was found in a rural area.

Andy J. McCauley Jr., 41, was taken into custody and faces a murder charge in connection to the death of Riley Crossman, the Morgan County Sheriff's Office said in a press release.

Earlier on Thursday, investigators found a body "positioned over an embankment in a rural mountain road section" in Berkeley County.

Riley Crossman

Sheriff K.C. Bohrer said at a news conference Thursday evening that detectives believe the body belongs to Riley, and an autopsy scheduled for Friday will determine if the remains are hers. Authorities have not said how she was killed.

Riley, 15, a student at Berkeley Springs High School, was reported missing on May 8 by her mother, Chantel Oakley, after she realized the girl did not show up for school.

Oakley told NBC's "Dateline" that she became worried when Riley did not come home from school at her normal time. Oakley said she tried texting her daughter, but the messages did not go through, and when she tried calling Riley it went straight to voicemail.

Erich May, superintendent of Morgan County Schools, said the district was "deeply saddened" by Riley's death.

"We have lost a cherished member of our school community," he said in a statement on Friday. "School counselors, social workers and clergy are in schools today to support students and staff, and we are sending additional resources home to the families of our students. ... The community has rallied around the Crossmans. We ask everyone to keep them in their thoughts and prayers."

McCauley, who was in a relationship with Oakley, was a person of interest "since Day One," Bohrer said at Thursday's news conference. McCauley was under surveillance when he agreed to speak with police and was then arrested, Bohrer said.