(CNN) -- A doctor in suburban Oklahoma City, Oklahoma, was arrested Monday and accused in the early morning death of his 9-year-old son, police said.

Dr. Stephen Wolf, 51, faces first-degree murder charges, said Nichols Hills, Oklahoma, Police Chief Richard Mask.

Third-grader Tommy Wolf was dead when authorities arrived at the family's home about 4 a.m. CT in response to several 911 calls, Mask said.

"It was obvious there had been some type of altercation" when police arrived, Mask said. Arriving officers disarmed Wolf, he said, but did not elaborate except to say a knife was found at the home.

Although the investigation is still under way, authorities believe the altercation may have begun in the boy's room "and proceeded from there" to other rooms, Mask said.

Mary Wolf, Stephen Wolf's wife and the boy's mother, suffered defensive puncture wounds to her hands and a wound to her mouth, and was being treated at a hospital, Mask said. Authorities believe she attempted to "intercede and protect her child," he said. Her wounds were not considered life-threatening.

The first 911 call came in at 3:53 a.m., from the Wolf family's next-door neighbor. Mary Wolf had run to the house for help, and the resident reported someone was knocking on the door, Mask said.

Mary Wolf made the second call, but hung up, possibly because she was defending herself, he said. She also made the third call, after police had arrived. Mask said tapes of the 911 calls would be released later.

"We are trying to put all the facts together," Mask said. The boy's death, he said, has had a "devastating" effect on Nichols Hills, a city of about 4,000 people in Oklahoma County in the central part of the state. "It's had a huge impact," he said.

Officials at the boy's school, Christ the King Catholic School, said teachers and students had been made aware of his death, CNN affiliate KOCO reported.

Stephen Wolf is listed as an internist in Oklahoma City. In his booking photo, on the Oklahoma County sheriff's Web site, a wound can be seen on his head.