MODESTO, Calif. (AP) – Scott Peterson pleaded innocent Monday to killing his pregnant wife and unborn son, as the district attorney filed murder charges and said he would probably seek the death penalty.

“I am not guilty,” a clean-shaven 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 just before Christmas.

“It’s hard for me to realistically believe it is anything but a death penalty case at this time,” Brazelton told ABC News.

Brazelton didn’t return messages left Monday by The Associated Press.

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

California law permits a murder charge for a fetus if a pregnant woman is slain, even if the fetus is not viable, said Hallye Jordan, spokeswoman for the state attorney general. The law has been on the books for about 30 years.

Documents filed by prosecutors said the killings happened at the Petersons’ home in Modesto between Dec. 23 and Dec. 24.

Peterson, a fertilizer salesman who has always maintained that he had nothing to do with his wife’s disappearance, was handcuffed and shackled when he entered the courtroom Monday. As Judge Nancy Ashley read the charges, Laci Peterson’s mother, Sharon Rocha, wept.

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 to Mexico. He has since been 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 AP on condition of anonymity. His arrest came just hours before DNA testing confirmed the identity of the two bodies.

Defense lawyer Kirk McAllister, who had represented Peterson before the arraignment and met with him in jail Saturday night, would only say there was a good explanation for the cash his client had. He declined to say why he was no longer representing Peterson.

In an interview with Time magazine, Peterson’s father, Lee, said “police have just bungled this investigation from day one.”