Authorities concluded Monday that a 7-year-old girl who was abducted from her bedroom more than three weeks ago is dead and said they will charge a neighbor with murder.

"I must conclude that Danielle van Dam is no longer living and was killed by her abductor," San Diego County District Attorney Paul Pfingst said during a news conference called to announce the charge.

David Westerfield, 50, who lives two doors down from the van Dam home, was arrested Friday and was being held without bail. He is scheduled to be arraigned Tuesday after prosecutors file the charges.

Pfingst said there were no other suspects.

Danielle was last seen Feb. 1 when her father put her to bed. Police believe she was abducted from her second-floor bedroom in the family's north San Diego home and launched an extensive search that stretched from Mexico to the Imperial County desert. The girl has not been found.

The prosecutor said he will file one count of murder with a so-called special circumstance — murder during kidnapping — that will carry the possibility of the death penalty or life in prison if Westerfield is convicted. Pfingst said no decision has been made about seeking the death penalty.

The enormous publicity surrounding the case, which failed to produce information leading to the girl, and the totality of the evidence "provides only one reasonable conclusion, and that is Danielle van Dam is no longer living," Pfingst said.

Danielle's disappearance had received nationwide attention as her parents, Brenda and Damon van Dam, clung to the hope she might be found alive.

Pfingst said he met Saturday in his office with the parents.

"It was difficult to bring out the word 'murder,"' he said. "Both parents were in tears."

The van Dams declined to speak with reporters after the murder charge was announced.

"They're maintaining their privacy but also want to thank anyone involved in the search. They're just continuing to try to find Danielle," family spokeswoman Sara Fraunces said.

Volunteers continue searching for the girl, but received instructions Monday about how to look for a body.

"That was pretty emotional for everybody," said George Rillo, a computer programmer from San Marcos who took the day off to help the search effort.

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

To try someone for murder without a body, prosecutors must establish a "reasonable probability" that the victim has died, said Justin Brooks, director of the California Innocence Project at California Western School of Law in San Diego.

"It's nowhere near as hard as proving something beyond a reasonable doubt, but it's a lot more than just showing blood stains," Brooks said.

Authorities have said they found traces of Danielle's blood in Westerfield's motor home and on an article of his clothing. They also confiscated child pornography from his home, Police Chief David Bejarano said. Prosecutors are deciding whether to file pornography charges, Pfingst said.

Prosecutors might also add an additional count of kidnapping when the charges are formally filed Tuesday before the arraignment, officials said.

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

Investigators began focusing on the self-employed engineer shortly after the girl's disappearance. He was at the same bar where Brenda van Dam partied with friends the night Danielle disappeared. Damon van Dam stayed home with their daughter and two sons.

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