(CNN) -- Police in suburban Seattle said Tuesday they have not ruled out the possibility of foul play in the disappearance of a 2-year-old boy who was reported missing after being left alone in a car by his mother.
According to police, Sky Metalwala's mother said she ran out of gas in Bellevue, just east of Seattle, leaving the toddler in the car while she took her 4-year-old with her to get help.
"She told us that her son was asleep, and that's why she chose to leave him in the car, because she couldn't carry both kids to walk to the gas station," Maj. Mike Johnson of the Bellevue Police Department told CNN's Brooke Baldwin.
Julia Biryukova, the mother, said the young boy was gone when she returned to the vehicle about an hour later, according to police.
"At this point, foul play has not been ruled out," Johnson said, adding that neither the mother nor the boy's father is a suspect. Police have no suspects, and no arrests have been made in the case.
Other than the boy's mother and his 4-year-old sister, no one has reported seeing the toddler in the past two weeks, according to police spokeswoman Carla Iafrate. She described the mother, who gave police permission to search around her home and car, as cooperative.
The father, Solomon Metalwala, who is separated from Biryukova, took a polygraph test Monday and was expected to take another Tuesday after results of the first one were inconclusive, said Sgt. Seth Tyler of the Bellevue Police Department.
He said the car door was unlocked when police got to it.
Authorities began their search around the vicinity of the vehicle but found nothing. They are canvassing the mother's apartment complex in Redmond, northeast of Bellevue, Tyler said.
Search-and-rescue experts brought in to assist told police they do not believe the boy got out of the car and wandered off, according to Johnson.
"So we're trying to look at other options," he said.
Early indications suggest that the car still had some gas in it when it was left and that it would run, he said. However, police have not done a forensic examination of the vehicle.
"Our primary concern right now is to locate Sky," said Johnson.
The toddler has brown eyes and short, dark hair and was wearing a dark green hooded sweatshirt and blue-and-gray striped pants when he was last seen.
The boy's parents, who separated last year, have a tumultuous relationship.
Biryukova has said she feared for her safety and that of her children around Metalwala, according to court records.
"I am told by my husband Solomon (and) his family that if I take any action towards custody of our children he will take them out of the country (and) I will never see them again," she wrote.
Metalwala responded, in court filings, that his wife suffered from mental health problems and was unable to care for the children on her own.
Both parents were charged in 2009 with reckless endangerment for leaving then 3-month-old Sky alone in their parked car. Court records show they completed court-ordered parenting courses following the incident.
CNN's Patrick Oppmann and Deanna Proeller contributed to this report.