A convicted sex offender pleaded not guilty Thursday to charges of kidnapping and raping a Northern California girl when she was 11 and holding her captive for nearly two decades.

The plea came as a surprise after an attorney said Phillip Garrido had made a deal with prosecutors to plead guilty. It would have sent him to prison for the rest of his life.

But Phillip Garrido's attorney, Susan Gellman, contended the grand jury was improperly selected and did not act appropriately during its proceedings. Gellman did not elaborate in court.

"There are issues about the process itself before the grand jury," said Judge Doug Phimister.

Garrido, who fathered the two children of victim Jaycee Dugard, made the plea to an amended indictment that added allegations of kidnapping of a person under 14, kidnapping for sexual purposes and other claims.

His wife, Nancy Garrido, also pleaded not guilty to the charges. The next hearing was set for May 5, and the trial for Aug. 1.

Both defendants were in court for the 10-minute hearing, wearing orange jail uniforms. They didn't speak, and neither showed much emotion during the hearing.

Dugard was snatched off her family's South Lake Tahoe street in June 1991 while walking to a school bus stop.

Authorities said she and her children were kept in a hidden backyard compound of tents and sheds, never attending school or receiving medical attention.

They finally resurfaced in August 2009 when Phillip Garrido took them to a meeting with his parole officer.

Garrido and his wife gave full confessions to authorities and expressed interest in plea bargains that would spare Dugard and her daughters _ now 13 and 16 _ from having to testify, said attorney Stephen Tapson, who represents Nancy Garrido.

Tapson, however, said he advised Nancy Garrido against pleading guilty unless prosecutors offer a deal that holds the possibility _ however remote _ that she would one day be freed from prison. He told reporters in the week before the hearing Thursday morning that Phillip Garrido was expected to plead guilty.

Phillip and Nancy Garrido were both charged with 18 counts of kidnapping, rape, false imprisonment, child pornography and committing lewd acts on a child.

If convicted on all counts, the maximum sentence for Nancy Garrido would be 181 years, while Phillip Garrido could get 431 years, according to El Dorado County Deputy District Attorney James Clinchard.

Dugard gave birth to her daughters when she was 14 and 17, and Nancy Garrido delivered the children, according to court documents. The girls knew Phillip Garrido was their father but grew up thinking Dugard was their older sister.

The mother and daughters rarely interacted with the outside world. Phillip Garrido ran a printing business, and Dugard assisted him in producing business cards, brochures and flyers, occasionally interacting with clients through email.

A few neighbors and customers would later report having seen the girls but not thinking much of it, even though they knew Garrido was a sex offender.

The FBI, police and volunteers searched in vain for the pretty blonde girl who was last seen wearing a pink wind breaker and pink stretch pants.

But they never came close to finding her, even though Dugard's stepfather gave an accurate description of the couple's car and of Nancy Garrido, and despite the fact that Phillip Garrido was being monitored by state parole agents because of his rape conviction.

Dugard's reappearance 18 years, four months and 16 days later came about almost as a fluke.

In the days before his arrest, Phillip Garrido had become more determined to tell people about the religious group he founded called God's Desire and a box he had built that he believed allowed him to speak with God.

During that time, he delivered a handwritten screed titled "Origin of Schizophrenia Revealed" to the FBI's San Francisco office.

But it was a visit to the University of California, Berkeley, that same day that caused his ragged family to unravel. He showed up at campus with his daughters and Dugard in tow, seeking a permit for a religious event.

Campus police officers became suspicious, and after running a background check realized he had been convicted of kidnapping and raping a woman in Nevada in 1977.

The Berkeley officers contacted Garrido's parole officer, who was surprised to hear that he had young daughters and ordered him to come in for a meeting.

Garrido complied and, for reasons still unknown, brought his wife, the girls and Dugard.

Dugard tried to conceal Dugard's identity, initially telling authorities she was hiding from an abusive husband in Minnesota and giving her name as Alyssa.

Wary investigators separated her from Phillip Garrido, who had described Dugard and the two girls as his nieces, and under further questioning he admitted kidnapping Dugard, who separately disclosed her identity, authorities said.

She was reunited with her mother the next day and has remained in Northern California with her and her daughters. She requested privacy and has not attended any of the court hearings. She is writing her memoirs, which are scheduled to be published in September.

The Associated Press as a matter of policy avoids identifying victims of sexual abuse by name in its news reports

However, Dugard's disappearance had been known and reported for nearly two decades, making impossible any effort to shield her identity when she resurfaced.

Dugard's case revealed problems with California's system for monitoring convicted sex offenders after it was determined parole agents had missed numerous clues and chances to find her.

She received a $20 million settlement under which the state acknowledged repeated mistakes were made by parole agents responsible for monitoring Phillip Garrido. California has since increased oversight of sex offenders.