San Diego ? Investigators concluded Monday that a 7-year-old girl who vanished from her bedroom more than three weeks ago is dead, and said they would bring murder charges against her neighbor.

“I must conclude that Danielle van Dam is no longer living and was killed by her abductor,” Dist. Atty. Paul Pfingst said.

David Westerfield, 50, who lives two doors down from the van Dams, was arrested Friday on suspicion of kidnapping and was jailed without bail. Authorities said they found traces of Danielle’s blood in Westerfield’s motor home and on a piece of his clothing.

That, combined with the fact that Danielle has not been found despite extensive publicity, “provides only one reasonable conclusion, and that is Danielle van Dam is no longer living,” Pfingst said.

The district attorney said he will file murder charges and a so-called special circumstance  murder during kidnapping  that will carry the possibility of the death penalty. Pfingst said no decision has been made about whether to seek the death penalty.

Pfingst said there were no other suspects.

Investigators also confiscated child pornography from Westerfield’s home.

Westerfield’s lawyer did not immediately return a call Monday. On Friday, Steven Feldman said only that he intends to “mount a vigorous defense.”

Danielle was last seen the night of Feb. 1, when her father put her to bed. Police launched an extensive search that stretched from Mexico to the desert 100 miles east of San Diego. Her disappearance was featured on “America’s Most Wanted” 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.

Westerfield, a 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 and was the only immediate neighbor who was gone when the search began.