The search for missing seven-year old Danielle van Dam took an ominous--although not--unexpected turn Friday when police arrested the girl's neighbor for her kidnapping. A twice-divorced mechanical engineer, David Westerfield, 49, has been the prime suspect in the three-week old case. He lives alone two doors from the van Dam home in the upscale San Diego suburb of Sabre Springs, where blonde, blue-eyed Danielle was abducted as she lay sleeping in her upstairs bedroom. Police remain unsure of Danielle's whereabouts, or whether the outgoing second grader, an avid T-ball player and Girl Scout, is still alive.

What they say they do know, based on lab results that came in Friday morning, is that DNA evidence links Westerfield to Danielle's disappearance. "Danielle's blood was found on an article of clothing that belongs to Mr. Westerfield, and also in his motor home," says San Diego Police Chief David Bejarano. He says DNA evidence was also found on an article of clothing in the girl's bedroom.

The saga of Danielle's disappearance began Feb. 1, when her father, Damon, put the girl to bed at 10:30 p.m. Danielle's mother, Brenda, was out with friends and returned home around 2 a.m. Brenda van Dam told police that upon her return, she shut her daughter's door so as not to awaken her, although she did not check on the child. The elder van Dams say they stayed up with their friends for about an hour, and then went to bed. They made a frantic 911 call to police at about 9 a.m. the next morning, upon discovering that Danielle was missing.

Investigators focused on Westerfield early on. A local tow-truck operator told police that he had towed Westerfield's mobile home out the sand in a remote area near the California-Mexico border the day after Danielle was reported missing. A full-scale search of the area, as well as hundreds of acres of nearby desert and canyons, found nothing.

Sources tell NEWSWEEK that police twice felt confident enough in the past weeks to take their case against Westerfield to the San Diego District Attorney, who pressed for additional evidence. Convinced that conclusive proof was forthcoming, the cops kept Westerfield under 24-hour surveillance. "We wanted to be ready to make an arrest, no matter what time of day or night, as soon as we got the DNA results back," says Bejarano.

Others have been watching Westerfield, too. The entire van Dam neighborhood has teemed with the news media since the day the story broke. Satellite trucks line the street; cameras are posed at the ready, capturing the daily, often tear-filled impromptu press conferences held by Damon and Brenda van Dam. And last week, the story took another twist. Local talk-radio shows were abuzz with allegations, leaked from "high-ranking law enforcement sources" that Damon and Brenda van Dam were active "swingers" who regularly participated in spouse-swapping.

The van Dams have not denied the allegations, and insist that stories of their alternative lifestyle "have nothing to do" with the disappearance of their daughter. Police aren't making any official comment on those reports. Nor do they have a theory behind Westerfield's alleged actions. "We've had a number of conversations with Mr. Westerfield. But, at this point we have no motive," says Bejerano. Westerfield did tell police that he danced with Brenda van Dam at the bar the night Danielle was abducted, although Brenda van Dam has said that is untrue.

In the meantime, the chance that Danielle will be found alive grow slimmer with each passing day. "As a father, I'm optimistic that at some point we will find Danielle, but on the law-enforcement side, we all know that is becoming less and less realistic," says Bejarano. Police continue to comb through more than six hundred tips, and volunteers will keep up their search in the desert outside of San Diego this weekend. As Damon and Brenda van Dam said a few minutes after news of Westerfield's arrest was made, "We are very happy that the police have made an arrest. But, the fact still remains that we don't have our daughter. We need to keep looking for her. Please help us find her.