OAKLAND -- The search for missing toddler Daphne Viola Webb intensified Thursday as investigators and cadaver dogs scoured an Oakland shoreline, hours after her father was arrested on suspicion of child endangerment.

Police said they arrested John Anthony Webb, 49, after he told them he left his 21-month-old alone in his vehicle with his elderly mother, who has dementia, when he went into a convenience store Wednesday. When he returned, he told police the girl was gone. The father is being held in Santa Rita Jail on $100,000 bail and is expected to be arraigned Friday afternoon.

"We are concerned about the relationship with the child and the father," said police spokeswoman Johnna Watson, adding that Webb was not a suspect and he had been cooperative with police.

Daphne Viola Webb
Daphne Viola Webb (Oakland Police Department)

Webb, who lived in Sacramento for a couple decades according to public records, was arrested in that city in 2001 on a felony charge for discharging a firearm with gross negligence and was sentenced to two months in a sheriff's work project, according to court records. In 2002, he was arrested on misdemeanor spousal battery and criminal threats charges. Those charges were dismissed the following year. He has no criminal record in Alameda County.

Webb and his family have not been available for comment since Daphne went missing. The child's mother is not a person of interest, police said.

Daphne's case is still being treated as a missing person and kidnapping incident, but investigators have targeted searches at her father's residence and a park where the pair often visited.

The father's story draws striking comparisons with another African-American toddler reported missing in Oakland four years ago. On Aug. 10, 2009, 5-year-old Hasanni Campbell, who lived in Fremont, vanished. His foster father, Louis Ross, told police he parked in a Rockridge neighborhood, taking his daughter into a shoe store while leaving Hasanni, who wore leg braces due to cerebral palsy, inside the car. When he returned, Hasanni was gone.

Eighteen days later, Oakland police arrested the boy's foster parents on suspicion of murder before releasing them days later due to lack of evidence. The pair have since left the state, and Oakland police believe Hasanni is dead.

A child abduction expert said there's a statistical basis for targeting parents early in investigations.

"Police are always on the right track when a stranger abduction is alleged (to) have suspicions that maybe it happened at the hands of a family member and was covered up," said David Finkelhor, director of the Crimes Against Children Research Center at the University of New Hampshire. He said parents often use stranger abductions as a ruse to cover up a crime against a child.

Each year, about 1,500 children die in the hands of their parents, while about 100 are abducted by strangers, he said.

"Children of that age don't experience that many stranger abductions," Finkelhor said.

Toddlers are usually taken by family members in custody disputes, he said. In rare instances, young women who cannot have their own children abduct kids, but often newborns. Stranger abductions are usually motivated by sex, and kidnappers target teens or preteens, he said.

Early Thursday afternoon, investigators set up crime scene tape and moved bystanders away from a Martin Luther King Jr. Regional Shoreline parking lot, near Oakland International Airport. Members of the Alameda County Sheriff's Search and Rescue team and at least two search dogs were on scene, while law enforcement boats scanned the water close to the shore.

It marked the second time in two days police searched the park, where investigators said Webb told them he spent a lot of time with his daughter. Police and FBI agents also searched Webb's apartment on Greenridge Drive.

Webb told police that just after 11 a.m. on Wednesday he left his 87-year-old mother and the toddler -- who is black, about 2 feet tall, weighing about 30 pounds and wearing an orange, two-piece pajama set with pink hearts and pink socks -- in his vehicle. He went into Gazzali's Supermarket at 79th Avenue and International Boulevard, where the store's clerk said Webb bought an energy drink and was in and out of the corner store quickly. Webb told police when he returned the girl was gone from the back seat.

Police are evaluating a resident's account from several blocks away from the market that a girl with similar clothing was seen with an unidentified black or Latino woman between 30 and 40 years old who had long, straight black hair and was wearing a light-colored shirt and jeans.

If it turns out to be a stranger abduction, Finkelhor said Daphne stands a good chance at surviving the ordeal.

"A child of this age, if abducted, has a good chance of survival because the primary motive (of the abductor) is to raise the child," he said. In addition, an abducted toddler of that age would have trouble identifying the perpetrator, which is often a motive for killing other abducted older children, he said.

Staff writers Harry Harris, Doug Oakley and Brittny Mejia contributed to this report. Contact Matthias Gafni at 925-952-5026. Follow him at Twitter.com/mgafni.