A gas can wasn't found in Biryukova's car, a detail that "could mean a lot of things," Bellevue police spokeswoman Iafrate told ABCNews.com Monday.
Her car showed no sign of forced entry, according to police, who stopped searching the wooded area near the car Sunday evening.
When Iafrate spoke to Biryukova on Sunday evening, "she was quite calm at that time and concerned."
"Over the years that I've been an officer, I'm struck by how people react to a stressful situation and there are many different reactions to stress. Some people are calm and some are hysterical," she said.
A 'Frustrating' Case
"There's not been a whole lot of progress in the investigation, and as you well know, that's really frustrating to us as well," Iafrate told reporters today. "So far we have only been able to locate one person who has seen Sky in the last two weeks and that was a neighbor."
Although one tipster called police after seeing Biryukova's car on the side of the road during the same time period police were notified that Sky was missing, the tipster said nobody was in the car.
Attempts by police to question Biryukova's 4-year-old, who is currently in protective custody, also failed to turn up any clues. She said her brother Sky was in the car.
"I'm hoping that someone's going to call us on a tip line and tell us something that's going to lead us to Sky," said Iafrate. "We're going to work day and night until we can solve the mystery."
Police are erecting three billboards to solicit tips from the public.
"Even if you think you didn't see anything, doesn't matter; we want to hear from you if you were on that road at that time," Iafrate said.
Searching for Sky Metalwala
Sky is half Indian and half Caucasian, with brown eyes and dark buzz-cut hair. He was last seen wearing a dark green hooded sweatshirt with blue and gray striped Carter's pants, the same outfit he's pictured in above.
Anyone who sees a child matching this description is asked to call 911 immediately. Police are urging anyone who might have traveled along 112th Ave N.E., between I-520 and NE 24th Ave N.E., Sunday morning between 7:00 a.m. and 10:00 a.m. to call Bellevue, Wash., police at 425-452-2564 or email email@example.com.