Danielle van Dam's neighbor pleaded not guilty to charges of murder, kidnapping and possession of child pornography Tuesday.

David Westerfield, 50, the lone suspect in the death of the 7-year-old girl, stood behind bulletproof glass and denied the allegations against him in state Superior Court. He remained in jail without bond.

Prosecutors charged Westerfield with a single count of murder with a so-called special circumstance — murder during kidnapping — that carries the possibility of the death penalty or life in prison if Westerfield is convicted. No decision has been made on whether to seek the death penalty, said San Diego County District Attorney Paul Pfingst.

Westerfield's attorney, Steven Feldman, has promised to mount a "vigorous defense." Judge Peter C. Deddeh denied Feldman's request Tuesday to impose a gag order in the case.

Danielle was last seen Feb. 1 when her father put her to bed. Police believe she was kidnapped from her second-floor bedroom in the family's north San Diego home. An ongoing search that has stretched from Mexico to the desert east of San Diego has failed to turn up any trace of her.

The girl's mother, Brenda van Dam, burst into tears as deputies brought her neighbor into the crowded courtroom. She held hands with her husband, Damon, throughout the arraignment.

Afterward, Brenda van Dam spoke tearfully to reporters outside her home.

"We've been asked again and again 'How are you feeling?"' she said. "All we can answer is that we miss Danielle desperately and the pain of her absence is absolutely unbearable."

She then urged the public to help with a massive volunteer search for Danielle scheduled for this weekend.

Westerfield, a self-employed engineer who lives two doors down from the van Dam home, was arrested Friday and jailed without bail. Pfingst said there are no other suspects.

The three-page complaint filed Tuesday against Westerfield did not provide specific dates for the alleged kidnapping and murder.

Danielle's disappearance received nationwide attention as her parents clung to the hope she might be alive and coordinated massive searches for her.

The absence of a body creates a legal challenge, but the San Diego County district attorney has successfully prosecuted four such cases, the most recent in August.

Authorities have said they found traces of Danielle's blood in Westerfield's motor home and on an article of his clothing.

Westerfield, a twice-divorced father of two grown children has a 1996 drunken driving conviction but no violent criminal history.

Investigators began focusing on him shortly after the girl's disappearance. He was at the same bar where Brenda van Dam partied with friends the night Danielle disappeared while her husband stayed home with their daughter and two sons.

By the next morning, Westerfield had set off for the beach and desert in his motor home and was the only one of the van Dams' immediate neighbors who was gone when the search began.

The charge of kidnapping a child under 14 carries 5-11 years in prison. The child pornography charge is a misdemeanor with a maximum penalty of a year in jail.

A hearing is scheduled for Wednesday to consider a request by news organizations to unseal search warrants in the case.

The Associated Press contributed to this report.