David Westerfield, a divorced self-employed engineer, was found guilty after a lurid trial in which the defense suggested that the swinging lifestyle of Danielle's parents put her at risk.
Prosecutors, however, said drops of the victim's blood on the suspect's jacket was a DNA-backed "smoking gun'' that jurors couldn't ignore.
Westerfield, 50, faces a possible death sentence that will be determined in a separate penalty phase that will begin next week. He was also convicted of possessing child pornography by a jury that deliberated for nearly 10 days.
Danielle was last seen Feb. 1, when her father put her to bed. Her nude body was found nearly a month later along a road outside the city, too decomposed to determine the cause of death or whether Danielle had been sexually assaulted.
Westerfield, who lived two houses away from Danielle, was placed under surveillance early in the investigation after authorities learned he was at the same bar as Danielle's mother and two of her girlfriends the night the girl vanished. He left on a long, meandering trip in his motor home early the next day as police and volunteers searched the neighborhood.
He later retraced his RV trip with police and made the unsolicited comment that "this would be a great place to dump a body,'' according to court documents.
The girl's blood was later found on one of Westerfield's jackets and her hair inside his home. Investigators said Danielle's blood, hair and fingerprints were also discovered inside the motor home.
The defense said there was no motive and suggested it was improbable that the 6-foot-2 suspect could have slipped into the girl's home in the dark and snatched her away without leaving evidence of his presence.
Defense lawyer Steven Feldman also noted that Danielle and her mother had once been in Westerfield's home for about 15 minutes as the girl sold him Girl Scout cookies, suggesting that's why her hair was found inside.
Feldman repeatedly suggested that someone else was the killer, noting that a fingerprint found in the van Dam home and a hair found on the girl were never identified.
The case captivated much of San Diego, with local television and radio stations broadcasting gavel-to-gavel coverage and talk-radio programs delving into the details.
Feldman argued that the lifestyle of Danielle's parents, which included marijuana use and spouse-swapping, exposed their home to people who might have been responsible for the girl's disappearance.
Damon van Dam, 36, testified that he kissed and "snuggled'' in bed with one of his wife's friends the night his daughter disappeared. He also said he and his wife smoked marijuana with her friends earlier in the evening.
Other witnesses said they saw Brenda van Dam and Westerfield "dirty dancing'' and being "huggy huggy'' at the bar that night. One said van Dam rubbed her hips and bosom against Westerfield as he giggled. Brenda van Dam denied she danced with him.
The van Dams said their lifestyle had nothing to do with their daughter's abduction and slaying. Brenda van Dam wept as she testified, and both she and her husband sometimes gazed downward when their lifestyle was brought up during the rest of the trial.
Prosecutors also called experts who described the DNA link between Danielle and the blood on Westerfield's jacket. One said the odds that another person would have the same DNA were at least 1 in 130 quadrillion.
Julie Mills, a clerk at a dry cleaner, also testified that Westerfield came to the store two days after Danielle vanished, arriving in his motor home to drop off the bloodstained jacket, two comforters and two pillow covers.
She said it seemed odd that — on a cold morning — he was barefoot and wearing only a T-shirt and shorts. Detectives later came to the dry cleaner and confiscated the items for testing.
Danielle's kidnapping preceded other frightening abductions this year, including those of Elizabeth Smart in Utah, Samantha Runnion in Orange County and Cassandra Williamson in Missouri. Smart remains missing; the rest were slain.