MODESTO, Calif. (AP) — Scott Peterson pleaded not guilty Monday to killing his pregnant wife and unborn son, as prosecutors filed charges against him that could bring the death penalty.

"I am not guilty," Peterson said during a brief arraignment in Stanislaus County Superior Court.

Prosecutors filed the murder charges hours before Peterson, 30, appeared in the Modesto courtroom. In the filing, District Attorney James Brazelton said Peterson acted "intentionally, deliberately and with premeditation" in killing 27-year-old Laci Peterson and Conner Peterson, the couple's unborn child.

Their bodies washed ashore last week about three miles from where Peterson said he was fishing in San Francisco Bay when his wife -- who was eight months pregnant -- vanished.

The charges against Peterson include the special circumstance that he committed more than one murder, allowing the district attorney to seek the death penalty. Brazelton said he would likely seek the death penalty.

"It's hard for me to realistically believe it is anything but a death penalty case at this time," he said.

Public defender Tim Bazar was assigned to the case after Peterson said he could not afford to hire a lawyer. The case was continued until a May 6 bail hearing.

Peterson was arrested Friday in San Diego County because detectives feared he might try to flee the country. He was being held without bail at the Stanislaus County jail.

When he was arrested, Peterson's naturally dark hair was reddish-blond and he had grown a goatee. He had $10,000 in cash with him in his car, said a law enforcement source who spoke to The Associated Press on condition of anonymity.

In an interview with Time magazine Sunday, Peterson's father, Lee, said police had "bungled" the investigation.

"You have a district attorney calling this a slam-dunk before there's even an arraignment," Scott Peterson's mother, Jackie, told the magazine. "I'm feeling like I'm living in Nazi Germany or the Soviet Union."