John Anthony Webb, 49, father of 21-month-old Daphne Viola Webb, was arrested Thursday as Oakland, Calif., police and the FBI used cadaver dogs to search Oakland's Martin Luther King Regional Shoreline Park for signs of the toddler, the Contra Costa Times reported.
Police said Webb was arrested on a suspicion of child endangerment charge and was being cooperative and not considered a suspect in what appeared to be a kidnapping.
Authorities searched Webb's Greenridge Drive home while he was held in Santa Rita Jail on $100,000 bond, the newspaper said.
"We are concerned about the relationship with the child and the father," police spokeswoman Johnna Watson said.
Daphne disappeared Wednesday evening after her father left her in the back seat of his sports utility vehicle while he went to buy an energy drink from a supermarket, the Oakland Tribune reported.
An elderly relative was in the front seat of the SUV at the time the child was taken by an unidentified black or Hispanic woman 30 to 40 years old, police said. Witnesses told police they saw the woman walk away from the car with the child.
Watson said investigators had questioned other family members, including Daphne's mother, whose name was not released. The relationship between Webb and Daphne's mother was not known.
The California Highway Patrol issued an Amber Alert for Daphne for Alameda, Contra Costa and San Francisco counties.